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SWCO Aug 2016 - La Niña Tracker

Friday, August 19, 2016

Oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) remain in the range of neutral conditions (Figs. 1-2). Seasonal forecasts and models identify the most likely scenario being a weak La Niña event forming sometime in late summer or fall 2016 and lasting through winter 2017. Some uncertainty exists regarding the specific timing of this event, as the equatorial sea surface temperature (SST) anomalies have not yet dropped into La Niña range and there is a lack of coordination between ocean and atmosphere (and in particular the lack of enhanced trade winds).

A closer look at the various forecasts and seasonal outlooks provides insight into the range of expectations for this La Niña event. On August 10, the Japanese Meteorological Agency saw below-normal equatorial convective activity and enhanced trade winds as indicative of the start of La Niña-favorable conditions, even while the SST anomalies were slow to swing more negative (cool) after the sustained warm period associated with El Niño conditions. The agency forecast a 70 percent chance of a La Niña event developing, but not until fall 2016. On August 11, the NOAA Climate Prediction Center (CPC) highlighted ENSO-neutral conditions in both ocean and atmosphere and continued to focus on tension between statistical and dynamical models, the former predicting a later onset and weaker event than the latter. The CPC forecast remains at a 55–60 percent chance of a weak La Niña event starting sometime between August and October 2016. On August 16, the Australian Bureau of Meteorology maintained its La Niña watch, albeit with slightly reduced confidence compared to the previous month, hedging slightly by stating “if La Niña does develop it is likely be weak.” The bureau maintained its forecast probability at a 50 percent chance of a La Niña event developing, noting that is approximately twice the normal chance of a La Niña forming. On August 18, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated the probability of a “borderline/weak” La Niña forming was just less than 60 percent (Fig. 3). The IRI forecasters noted that until the atmosphere cooperates (i.e., the enhanced trade winds show up), the ENSO-neutral holding pattern will remain. The North American multi-model ensemble characterizes the current model spread and highlights the variability looking forward to 2017, but the ensemble mean hovers close to weak La Niña status for fall and winter of the coming year (Fig. 4).

The Southwest is in a holding pattern regarding La Niña but will likely see the effects of a weak La Niña this winter. Forecasters are likely already integrating the influence of the drier-than-average signal associated with La Niña into long-term precipitation and temperature forecasts and seasonal outlooks (Fig. 5a-b), and researchers are preparing to track both the timing and intensity of this event in relation to precipitation, temperature, snowpack, and water supply over the coming year. 

Given the dry climate of the Southwest, a weak La Niña event does not necessarily deviate far from the seasonal climatology of the region, but while ENSO-neutral winters have a wider range of precipitation values observed over winter, La Niña winters skew more dry. Even a weak La Niña event is likely to suppress winter precipitation totals in the Southwest, which is unwelcome news given the underperformance of last year’s El Niño winter and the longer-term effects of multi-year drought.

El Niño Recap & La Niña Outlook - May 2016

Saturday, May 21, 2016

El Niño Recap & La Niña Outlook

This El Niño event was one of the strongest ever recorded (Fig. 5), and if past performance was any indication of what was expected for the Southwest, the region should have seen above-average precipitation over much of the cool season (winter and spring). The Southwest generally saw lower-than-expected precipitation totals that were much closer to average, or even below average in some cases.  There are several reasons why this event did not meet expectations. One explanation is the difficulty of predicting highly variable weather events within the context of climate. In the case of the El Niño event of 2015–2016, a ridge of high pressure diverted moisture away from the Southwest during the prime time we might have expected to see increased activity (see El Niño tracker in April 2016 SWCO for details). Another reason is related to the use of analogs, past strong events, such as the El Niño event in 1982–83 or 1997–98). This El Niño event looks to be a clear outlier compared to most other observations that quantify the relationship between the ENSO index value and precipitation anomalies (Fig. 6). This analysis is hampered by limited sample size, which means making broad pronouncements about these patterns is problematic until there are more observations of strong El Niño events to compare to this event, and more data to feed into seasonal forecasts and outlooks. A final reason for the recent El Niño falling short of expectations is the relative infancy of the science of El Niño. The climate and atmospheric/oceanic science community is still developing its understanding of El Niño and the influence of the Arctic Oscillation Index or the Pacific Decadal Oscillation. Experts in these fields will certainly look to this El Niño event to determine what additional information can be gleaned from an event that, by all accounts, could have blanketed the Southwest with regular and steady winter precipitation. Instead, warm and dry conditions dominated throughout much of the cool season in the Southwest, even while the El Niño event performed closer to expectations across most of the globe (Fig. 7).

Perhaps just as importantly, this discrepancy between seasonal outlooks and forecasts and the observed weather of the cool season did not take place in a vacuum. Long-term drought has affected the Southwest throughout much of the 21st century, and the prospect of a strong El Niño event generated considerable hope and optimism for the potential positive impacts of above-average precipitation. This optimism was augmented by media-fed narratives about the potential for extreme precipitation during a strong El Niño event that did not include the necessary caveats associated with most scientific models and forecasts. Still, it was generally understood that a single strong year would not “fix” long-term drought, but that it might at least bend the curve back towards some modicum of recovery. Near-average cool-season precipitation was disappointing when held up to these expectations but was much wetter than would be expected in a typical La Niña winter, a comparison that will be all the more salient by this time next year.

A strong El Niño event is typically associated with increased precipitation across the cool season in the Southwest, but there is a practical limit to how much additional precipitation a desert environment might experience, even in a record El Niño year. Conversely, a La Niña event is associated with decreased cool-season precipitation in the Southwest, somewhat more reliably in terms of forecasts and predictions; layering a dry signal (i.e., La Niña) onto an already dry climate may produce a more consistent result compared to layering a wet signal (i.e., El Niño) onto a dry climate (Fig. 8). The correlations between ENSO status and precipitation anomalies do generally follow this pattern; La Niña events are more reliably dry than El Niño events are reliably wet, and there is considerable variability between wet and dry in ENSO-neutral years. The El Niño event of 2015–2016 was decidedly average and a likely outlier from previous (and subsequent) El Niño events. The La Niña conditions forecast for 2016–2017 are much more likely to produce drier-than-average cool season precipitation totals, with implications for long-term drought in the Southwest.

El Niño Tracker - May 2016

Friday, May 20, 2016

El Niño conditions continued for a 15th straight month, but the peak intensity has long since passed and the event is moving toward ENSO-neutral status. Forecast discussions focused on the decline of atmospheric and oceanic anomalies that characterize an El Niño event, many of which are trending towards—or have nearly reached—ENSO-neutral status. Seasonal ENSO outlooks and forecasts have coalesced around the likely transition to La Niña conditions in fall or winter 2016. The spring predictability barrier—a time during seasonal transition that introduces a high degree of uncertainty into seasonal forecast models—makes identifying the exact timing of this transition difficult, but most models and forecasts center on the general framing of “Not if, but when?” regarding La Niña in 2016.

On May 10, the Australian Bureau of Meteorology maintained its outlook at La Niña Watch status, noting that El Niño conditions had weakened to borderline neutral status and that there was a 50 percent probability of a La Niña event developing in 2016. On May 12, the Japan Meteorological Agency identified a decaying El Niño event that is expected to weaken to neutral conditions by late spring followed by a developing La Niña by summer 2016. On May 12, the NOAA-Climate Prediction Center (CPC) extended its El Niño Advisory and its La Niña Watch. The CPC identified current atmospheric anomalies as reflecting an ongoing but declining El Niño event, while oceanic anomalies were much more indicative of ENSO-neutral status. The CPC forecast an end to El Niño by early summer (i.e., a return to neutral conditions), with a 75 percent probability of a transition to La Niña in fall or winter 2016. On May 19, the International Research Institute for Climate and Society (IRI) and CPC forecasts described a rapidly declining El Niño event, with La Niña conditions more than likely developing by late summer (Fig. 3). The North American multi-model ensemble shows the current decline from strong to moderate El Niño status over the past few months, as well as the possibility of a relatively rapid swing to weak to moderate La Niña conditions by summer (Fig. 4).

El Niño Tracker - March 2016 - Time Winding Down for El Niño in the Southwest

Friday, March 18, 2016

Originally published in the Mar 2016 CLIMAS Southwest Climate Outlook

El Niño conditions continued for a 13th straight month, but the peak of this event has passed. Monitoring and forecast discussions emphasize strong positive sea surface temperature (SST) anomalies (Figs. 1–2) and enhanced convective activity in the central and eastern Pacific. These positive temperature anomalies are waning, and trade wind activity is increasing, indications that this El Niño event is on the decline. Most forecasts emphasize this event will continue through spring or early summer before returning to ENSO-neutral status. There is also the possibility of swinging to La Niña conditions later in 2016, although there is considerable model and forecast uncertainty regarding the chances of La Niña vs. ENSO-neutral conditions.

On Mar. 10, the Japan Meteorological Agency identified ongoing El Niño conditions that had peaked and were actively decaying and expected to weaken to neutral conditions by summer.  On the same day, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, identifying current atmospheric and oceanic anomalies as reflecting a strong El Niño that will likely persist through most of the spring before transitioning to ENSO-neutral conditions in late spring or early summer. On Mar. 15, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, but noted a slow and steady decline, with decreasing positive temperature anomalies and near-normal trade winds as two key indicators of this event’s ongoing deterioration. On Mar. 17, the International Research Institute for Climate and Society (IRI) and CPC forecasts described mixed signals regarding El Niño, with zonal winds and SSTs in decline, while convective activity and the Southern Oscillation Index (SOI) remained strong. The IRI/CPC forecast still identifies a return to ENSO-neutral conditions by summer, with a 50 percent chance of transition to La Niña conditions later in 2016 (Fig. 3), but also points out that the spring predictability barrier will affect our certainty regarding ENSO-neutral vs. La Niña outlooks. The North American multi-model ensemble currently shows a strong event extending into early spring with gradual weakening to neutral conditions by early summer (Fig. 4).

This El Niño is not over; atmospheric and oceanic conditions are still indicative of a strong El Niño event. The CPC/IRI forecast noted this fact, stating that “El Niño is not done yet,” and that at a global scale, strong signals are still associated with El Niño, particularly in Brazil and southeast Asia (Fig. 5). In the southwestern U.S., we are nearing our dry season, meaning limited time remains for additional El Niño-influenced precipitation events of significance.

The IRI/CPC forecast also made note of the lack of “typical teleconnections” in this El Niño event. In the Southwest, for example, winter precipitation has been sparse following the storms of early January. These storms were exactly the sort of events expected in an El NIño year, but they were followed by a persistent ridge of high pressure that set up and limited the influx of additional moisture into the Southwest. This diverted moisture resulted in well above-average precipitation in the coastal northwestern U.S. and northern California, even while the Southwest was drier than normal (Fig. 6), a pattern which more closely aligns with La Niña. This occurred at an especially inopportune time in terms of southwestern climate patterns, as it effectively limited the opportunity for El Niño-associated storms during much of the the winter season. Sub-seasonal variability limited El Niño’s potential, and with the Southwest already characterized by dry conditions in a normal year, conditions that limit opportunities for precipitation can cut into seasonal totals significantly.

Next month’s issue will include a seasonal recap of El Niño and comparisons to seasonal averages as well as other El Niño events, but this high pressure ridge is likely one of the major reasons why the Southwest (and Arizona in particular) have not seen as frequent or as intense precipitation events as were forecast in seasonal outlooks. These forecasts and projections were dependent on the influence of a strong El Niño signal at a climate timescale (i.e., how these events cluster over years or decades), without the benefit of foresight of how a persistent high pressure ridge operating at a weather timescale (i.e., days or weeks) would knock the precipitation signal out of alignment for weeks on end.

2015-2016 El Niño Tracker - Feb 2016

Monday, February 22, 2016

Originally published in the Feb 2016 CLIMAS Southwest Climate Outlook


El Niño conditions continued for a 12th straight month, but we have passed the peak intensity of one of the strongest El Niño events on record. This does not mean that El Niño is over, though. Despite the recent warm and dry conditions in the Southwest, we are likely to see more weather events associated with El Niño conditions through spring 2016. In monitoring and forecast discussions, we continue to see persistent sea surface temperature (SST) anomalies (Figs. 1–2) and enhanced convective activity in the central and eastern Pacific, and most models forecast that this El Niño event will continue through spring or early summer. Precipitation and temperature outlooks mirror this forecast, calling for increased probabilities of precipitation across most of the southern U.S.

On Feb. 10, the Japan Meteorological Agency identified ongoing El Niño conditions as having passed their “mature” stage in the equatorial Pacific and predicted that this remarkably strong event would gradually weaken to neutral conditions by summer.  On Feb. 11, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory and identified the current atmospheric and oceanic anomalies as reflecting a strong El Niño that will persist through most of the spring before transitioning to ENSO-neutral conditions in late spring or early summer, with increasing chances of La Niña conditions by early fall. On Feb. 16, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, but noted that deceasing temperature anomalies and building trade winds are indicators of this event’s gradual decline. On Feb. 18, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated a gradual weakening of El Niño from late spring into summer (Fig. 3), and reiterated that this El Niño would likely gradually decline, with lingering effects and impacts through spring 2016. The North American multi-model ensemble currently shows a strong event extending into early spring with gradual weakening to neutral conditions by late spring or early summer (Fig. 4).

In the Southwest, seasonal forecasts and past events suggested we should see well above-average cumulative precipitation totals throughout our cool season (Oct–Mar). However, the past 30–40 days of mostly warm and dry conditions, including numerous record-setting high temperatures combined with the melting of our previously abundant mountain snowpack, makes it hard not to feel like this El Niño is a “bust.” Is this a fair assessment, or does this simply reflect the difficulty of interpreting climate events (e.g., El Niño conditions) on a weather timeline? In previous discussions, we’ve highlighted the fact that we should expect periods of inactivity between storms, but we were hopeful those inactive periods would be on the order of days to a week, not weeks to a month. Even so, the default state for the desert Southwest is dry, so even a strong El Niño event can only alter that system so much, and past events do show periods of extended inactivity. Precipitation during the 1997–1998 El Niño event (strongest on record) was well below average in January 1998 (Fig. 5), with an extended run of dry days before it roared back to life from February through April 1998 (Fig. 6). If we look at cumulative cool-season precipitation during our current El Niño event (October 2015 – January 2016), our precipitation totals are at or above average (Fig. 7), and January 2016 was less dry than it may have seemed thanks to an active first week of the month (Fig. 8).

Even though the 2015–2016 El Niño event peaked in December 2015, the impacts in the Southwest lag behind this spike in intensity, which means we look to late winter and early spring as the most likely times for increased storm activity associated with the El Niño signal. We won’t be able to fully evaluate the 2015–2016 El Niño event until we know how much rain and snow fell over the entire cool season, and given past events, our best bets for seeing above-average precipitation will be in February and March. In the short term, we are left waiting for the jet stream to shift to a favorable pattern that funnels moisture into the Southwest, rather than directing it around us. 

¿Cómo se determina la fuerza de El Niño?

Tuesday, February 2, 2016

Existen varios índices o indicadores para seguir el desarrollo de ENSO (La Circulación del Sur El Niño) a través del Océano Pacifico y para determinar si los patrones atmosféricos reflejan las condiciones típicas de El Niño, La Niña, o condiciones neutrales. Algunos índices solo toman en cuenta la atmósfera, por ejemplo el índice “Southern Oscillation Index.”  Otros solo examinan el océano (por ejemplo “Niño 3.4 index,”) y algunos examinan la combinación de ambos (por ejemplo el “Multivariate ENSO Index.”)  Todos los índices tienen diferentes fortalezas y debilidades, pero los índices que se basan en el océano tienden a reflejar la evolución lenta de ENSO, los patrones de los cambios en la temperatura superficial del océano, los cuales pueden tener gran efecto en los patrones del tiempo globales por muchos meses y estaciones.

El Centro de Predicción Climático del NOAO usa el Índice Oceánico El Niño (ONI) – la media actual de las anomalías de 3 meses de la temperatura superficial del mar en una parte clave del mar ecuatorial Pacifico desde al oeste de la línea de fecha internacional hacia 120 longitud oeste.

Seguimiento de las temperaturas del mar de esta región es buena indicación si la convección (impulsada por aguas cálidas) se está cambiando y se puede cambiar atípicamente más lejos hacia el oriente a través el ecuador durante las condiciones de El Niño, o lejos hacia el oeste durante los eventos de La Niña.  Los valores numéricos de ONI van desde -2.5 lo cual indicaría un evento fuerte de La Niña, hasta 2.5, lo cual indicaría un evento fuerte de El Niño.  El NOAA-CPC hace distinción entre la aparición de las condiciones de El Niño o La Niña – valores numéricos de ONI de +.5 (El Niño) o de -.5 como límite en la escala mensual además de otras indicaciones atmosféricas como cambios en los vientos y patrones de lluvia comparado con un evento bien desarrollado que puede tardar por muchos meses o estaciones.  Un evento requiere que los valores numéricos de ONI sean más que los límites de +0.5 o -0.5 por lo menos cinco meses consecutivos.  (Más detalles en climate.gov)

El Niño Tracker - Jan 2016

Friday, January 22, 2016

El Niño conditions continued for an 11th straight month, putting us squarely in the middle of a strong El Niño event that will be among one of the strongest events on record. Forecasts focused on the persistence of sea surface temperature (SST) anomalies (Figs. 1–2) and weakened trade winds, enhanced convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling. Models continue to forecast a strong El Niño event that will last through spring 2016, but we are starting to see signs of decline in the overall strength of the event.

On Jan. 12, the Japan Meteorological Agency identified ongoing El Niño conditions as having reached their “mature stage” in the equatorial Pacific in November–December 2015, with likely gradual weakening during the months ahead. On Jan. 14, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory and said the current atmospheric and oceanic anomalies reflect a strong El Niño that will persist through most of the spring, transitioning to ENSO-neutral by late spring or early summer. The CPC noted, however, that the “exact timing of the transition is difficult to predict.” On Jan. 19, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, with the event likely having peaked and ocean temperatures showing signs of gradual cooling. On Jan. 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated that all oceanic and atmospheric variables were indicative of a strong El Niño event, with consensus centering on strong El Niño conditions that will persist through spring 2016 (Fig. 3). The IRI/CPC briefing also indicated El Niño strength peaked in November–December, but that this was a “broad peak” with a gradual decline and the El Niño event would remain strong through late spring 2016. The North American multi-model ensemble currently shows a strong event extending into 2016 with gradual weakening heading into spring and summer (Fig. 4).

 

So what does this mean for the region? Even though forecasts are looking at the eventual decline of the El Niño signals, we are in the middle of a strong El Niño event. For the Southwest, the current seasonal forecasts and past events suggest we should see well above-average cumulative precipitation totals throughout our cool season (October–March), but we should also expect periods of inactivity between storms. Even though the 2015–2016 El Niño event “peaked” in November-December, we see impacts in the Southwest as they lag behind this spike in intensity, which means that we look to late winter and early spring as the most likely times to see increased storm activity associated with the El Niño signal. This doesn’t mean we can’t or won’t see increased activity outside of this window, but the default state for the desert Southwest is dry; even a strong El Niño event can only alter that system so much. We won’t be able to fully dissect and judge the 2015–2016 El Niño event until we see just how much rain and snow fell over the entire cool season. Given what we know about past events, our best bets for receiving above-average precipitation will be in February and March, or even April.  


Looking at the 1997–1998 event—the strongest El Niño event on record—most of Arizona and New Mexico received below-average rain and snowfall for all of January before returning to normal or above-normal precipitation in February and March (Figs. 5–8).

El Niño Tracker - Dec 2015

Friday, December 18, 2015

El Niño conditions continued for a 10th straight month, and models continue to forecast a strong El Niño event that will last through spring 2016 and remain strong through the early part of the year. Forecasts focused on the persistence of sea surface temperature (SST) anomalies (Figs. 1–2) and weakened trade winds, enhanced convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling. Notably, the SST values in the Niño 3.4 region were at or above the record values in November. Climate scientists have been quick to point out that numerous factors contribute to the overall strength of El Niño, but we are certainly seeing one of the strongest events on record.

Image Source - Australian Bureau of Meteorology

Image Source - NOAA/NWS - Climate Prediction Center

On Dec. 8, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, with the event having likely reached its peak. On Dec. 10, the Japan Meteorological Agency identified ongoing El Niño conditions as having reached their “mature stage” in the equatorial Pacific and “remarkably above-normal” SST anomalies and atmospheric convective activity. The agency projected that El Niño would remain in place through spring 2016 before transitioning to ENSO-neutral by summer. Also on Dec. 10, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory and identified the current atmospheric and oceanic anomalies as reflecting a strong El Niño event that will be one of the three strongest events on record. CPC models indicate the El Niño event will persist through winter, with a transition to ENSO-neutral conditions by late spring or early summer. On Dec. 17, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated that all oceanic and atmospheric variables were indicative of a strong El Niño event, with consensus centering on strong El Niño conditions that will persist through spring 2016 (Fig. 3).   The North American multi-model ensemble currently shows a strong event extending into 2016 with gradual weakening heading into spring (Fig. 4).

Image Source - International Research Institute for Climate & Society

Image Source - NOAA/NWS - Climate Prediction Center

So what does this mean for the region? Seasonal forecasts and past events suggest we should see well above-average cumulative precipitation totals throughout our cool season, but we should also expect periods of inactivity between storms. Past events also suggest the best bets for seeing above-average precipitation will be in February and March, and perhaps later in January. Looking at the 1997–1998 event—the strongest El Niño event on record—most of Arizona and New Mexico received above-average precipitation in December but below-average rain and snowfall for all of January before returning to normal or above-normal precipitation in February and March (Figs. 5–8). At this point, we know a strong El Niño event is underway, and it will likely have a number of projected impacts on the Southwest (and the world), but we will need to wait until seasonal totals are in to accurately gauge the impact of El Niño.

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker


To provide data and analysis regarding possible impacts of El Niño on the Southwest, CLIMAS created an El Niño hub: climas.arizona.edu/sw-climate/el-niño-southern-oscillation

Please contact Dan Ferguson or Ben McMahan for more information

2015 - Eastern Pacific Tropical Storm Recap

Friday, December 18, 2015

The 2015 eastern Pacific tropical storm season was one of the most active seasons on record, with 18 named storms and 13 hurricanes, nine of which reached “major” hurricane status (category 3 or greater). We also saw the strongest hurricane on record, Patricia, in the eastern Pacific in late October, and the latest-forming major hurricane on record, Sandra, in late November (see NOAA’s National Hurricane Center for more details). This meets or exceeds the high end of the NOAA-Climate Prediction Center (CPC) seasonal forecast (from May 27), which predicted 15 to 22 named storms, seven to 12 hurricanes, and five to eight major hurricanes. The eastern Pacific hurricane forecast was tied to the ongoing El Niño forecast discussion, as conditions linked to El Niño (e.g., decreased wind shear in the tropical Pacific) also favored increased hurricane frequency and intensity in the Pacific region. Conversely, the Atlantic hurricane season was relatively quiet, with 11 named storms, four of which became hurricanes, including two major ones. This was mostly in line with NOAA-CPC projections of six to 10 named storms, one to four hurricanes, and up to one major hurricane. 

The season started off early and strong with two major hurricanes, Andres and Blanca, forming before June 1—Blanca brought considerable moisture into the Southwest—and Hurricane Carlos forming in early June. This start ran counter to the expected early season pattern in which hurricanes remain in the Pacific Ocean and generally head west. Few storms made direct landfall as hurricanes, but numerous systems made their presence felt by driving significant moisture into the Southwest, making substantial contributions to monthly seasonal precipitation totals. The season also was characterized by some relatively anomalous events, in particular, the record-breaking Patricia, which formed very quickly off the coast of Mexico before charging ashore in late October, and the late-forming Sandra. It remains difficult to provide direct attribution of El Niño as the primary cause of specific tropical storm events, but this elevated tropical storm activity and intensity are exactly the sort of patterns that we expect, given the influence that El Niño conditions were forecast to have on the eastern Pacific tropical storm season.

El Niño and Media Coverage in the Southwest

Friday, December 18, 2015

What do wildflowers, hantavirus, downhill skiing, locusts, and floods all have in common? The answer is El Niño in the Southwest. These subjects represent a small sample of media stories written during the last 33 years that connect regional impacts to the El Niño phase of the El Niño-Southern Oscillation (ENSO) and help illustrate an evolution in our understanding of the significance of El Niño to the region. 

El Niño was documented as early as the 19th century by sailors who noticed that in some years, often around Christmas, a warm ocean current off the coast of Peru would bring changes to the regional marine ecosystem. But modern media coverage didn’t begin until the 1982–83 El Niño event. This event was particularly strong, and many scientists took note, enticed by the possibility of associating regional climate patterns with ENSO, as this development held the key to future climate forecasting. 

Upon reviewing all newspaper articles that reference El Niño impacts in the Southwest, three different phases of scientific coverage emerge. During the first phase, from the early 1980s through 1996, the science of ENSO was still fairly new and most stories discussed the general global, national, and sometimes regional impacts of El Niño. The second phase began during the strong 1997–98 El Niño event. The number of articles about El Niño in the region drastically increased at this time and referenced regional impacts as they were happening or a few months later. During the third phase, 1999–2014, journalists tried to use El Niño as a tool to predict future impacts that might occur in the Southwest. 

Phase #1 – Early ENSO Science and Impacts: The first phase was characterized by a handful of articles that were general in scope and discussed the dynamics of the ENSO cycle. For the Southwest, floods and above-average precipitation usually made the news. As this phase progressed, growing scientific evidence allowed for greater attribution of regional impacts in the region to El Niño, and the media slowly started to cover the story. The first news article was written in June 1983. It discussed regional flooding patterns across the U.S. and described the large snowpack on the verge of melting in the Southwest[1].  During this first phase, ENSO became a recognized phenomenon and the general idea that El Niño brought cooler, wetter weather to the region became fairly well established. However, many of the impacts attributed to El Niño were underdeveloped (e.g., killer bees migrating from Arizona to California[2] and the appearance of bubonic plague in New Mexico[3]) This was still early on in our understanding of the predictability of El Niño itself and many news articles grappled with how to cover long-range forecasting. 

Phase #2 – Attribution of El Niño Impacts in the Southwest: The second phase began during the very strong 1997–98 El Niño event. A substantial increase in media coverage occurred then, compared to prior events, with more than 100 news articles referencing impacts in the Southwest. By this point, researchers better understood the science of El Niño and its regional impacts. This meant increased attribution of weather and climate events to the ENSO cycle in the media, starting with coverage of Hurricane Nora, which “deposited two years’ worth of rain on the small town of Yuma”[4] in fall 1997. El Niño stories that winter discussed huge storms that dumped heaps of snow on ski slopes in Taos, New Mexico[5], but also buried sheep and cattle near Roswell[6], and brought heavy rain to Arizona in February and March[7]. This above-average precipitation promoted vegetation growth across the Southwest, translating into high pollen counts[8] and brightly blooming wildflower patches in Arizona[9]. The healthy desert vegetation also brought droves of locusts to western Arizona in the spring of 1998[10]  and boosted deer mice populations, which led to several occurrences of hantavirus in humans in the Four Corners region[11]. Media attention shifted in tone as the 1997–98 El Niño event progressed. Over time, a popular sentiment developed: “Oh, just blame it all on El Niño.”[12] Stories focused on the negative impacts of El Niño, and it often became a scapegoat for everything from the San Francisco Giants not getting enough practice time during spring training[13] to increases in food prices[14].

Phase #3 – The Media Race to Predict the Next El Niño: The strong 1997–98 El Niño generated a lot of scientific and media interest in predicting the next event. The third phase of media coverage was characterized by an effort to stay ahead of the curve and be the first to prepare the region for the impacts of another El Niño. This phase characterizes a time when scientists and journalists were still learning about the different flavors of each El Niño. Some were weak (2004–05) or moderate (2002–03), some quickly fizzled out (2006–07), and some were predicted but never actually started (2014). Each of these different events influenced regional weather patterns in distinct ways and climate information providers weren’t always able to clearly communicate the nuances to the media. Many news articles talked up the potential impacts of El Niño leading up to events (e.g., “Out and about: Dreaming of a white Christmas”[15]) only to carry disappointed headlines a few months later (e.g., El Niño rain turns out to be El Floppo”[16]).

It seems that we are currently beginning a new phase of El Niño media coverage with the 2015–16 event. Scientists have an improved understanding of the range of El Niño impacts and can better attribute certain weather events and occurrences to the ENSO cycle. In addition, this information has been translated into local news sources. While some national media outlets and climatologists have portrayed the 2015-16 El Niño as Godzilla[17], not one article referencing Arizona or New Mexico has characterized it as a monster. Perhaps that’s because El Niño means a lot of positive things for the region. Despite potential hazards, the desert could use some cooler, wetter weather, especially in contrast to the multi-year droughts that have characterized much of the 21st century thus far. But possibly it’s also because on a regional level, scientists and the media are better understanding and representing what El Niño means for the Southwest.


  1. “Summer floods seen as threat to much of nation.” The Washington Post. June 3, 1983.
  2. “Environment watch.” The Age. October 25, 1993.
  3. “And now for the weather: Two years from today there will be rain.” The Times. March 6, 1996.
  4. “International news: El Niño pours could water on LA routine.” The Guardian. September 27, 1997.
  5. “El Niño smiles on ski resort.” St. Louis Post-Dispatch. December 14, 1997.
  6. “El Niño gets the blame for weirdness.” USA Today. January 8, 1998.
  7. “It moved like a conveyor belt, hit like a train.” The Ottawa Citizen. January 15, 1998.
  8. “El Niño triggers sneezing season, pollen gets kicked up early.” USA Today. February 23, 1998.
  9. “El Niño’s good side: Wildflowers.” The New York Times. March 30, 1998.
  10. “Earthweek: Diary of a Planet.” The Toronto Star. April 25, 1998.
  11. “Lethal virus borne by mice makes return in West.” The New York Times. June 25, 1998.
  12. “Oh, just blame it all on El Niño.” Calgary Herald. July 13, 1998.
  13. “Giants expect wealth, stadium raises Magowan’s hopes.” San Jose Mercury News. February 22, 1998.
  14. “El Niño boosts produce prices.” The Toronto Star. April 22, 1998.
  15. “Out and about: Dreaming of a white Christmas.” The Santa Fe New Mexican. November 30, 2006.
  16. “El Niño rain turns out to be El Floppo.” East Valley Tribune. February 23, 2007.
  17. “Latest forecast suggests ‘Godzilla El Niño’ may be coming to California.” Los Angeles Times. December 15, 2015.

El Niño and Vector Borne Disease - What do we know about mosquitos, disease, and climate?

Monday, December 14, 2015

We are usually able to enjoy the patio by October, but the mosquitoes were still biting. What does the science tell us about El Niño and mosquito-borne disease? Short answer: it’s complicated. 

With respect to mosquito-borne disease, we tend to think about a mosquito season; the period of the year during which mosquitoes are active. For diseases like West Nile virus, the cycle starts when mosquitoes bite birds, infecting them with the disease. Eventually, often in late summer and early fall, enough mosquitoes and birds are infected that the disease spills over into human and horse populations. This requires that there are enough infected mosquitoes and that these mosquitoes survive long enough to become infectious and bite humans or horses. 

That gets us back to the mosquito-season. Immature mosquitoes—egg, larval, and pupal stages—require water to compete their life cycle. This water is provided both by precipitation and by human behavior, collecting in green pools, unprotected water storage, clogged gutters, or saucers under plants. Temperature drives how quickly an immature mosquito becomes an adult; typically, warmer temperatures speed up development. Another important piece is adult mosquito survival and host-seeking activity, both of which are mediated by humidity. Thus, the duration and intensity of any year’s mosquito season is going to be strongly influenced by temperature and precipitation. 

This year, with respect to precipitation, we had a wet June but then a normal July–September rainfall. The rains are expected to remain above-average through the winter. Despite the mosquitoes we experienced this summer and fall, the implications of the summer lull in precipitation are unknown. Because of the ramping up of West Nile virus in the bird-mosquito cycle, we might actually escape a bad year and hopefully, the bird-mosquito transmission cycle was broken and won’t have enough time (enter the effect of cooler winter temperatures) for it to build up again and spill over to humans. 

Research results are mixed, being highly dependent on the disease of concern and the region of study. Intuitively we know there must be an association between climate and vector life cycles, as the life cycle of invertebrates are often tightly associated with weather. However, with urban mosquitoes like the Culex species that transmit West Nile in the United States and the Aedes species that transmit dengue and chikungunya, human behavior plays a role in mediating exposure to mosquitoes, the availability of breeding sites, and even mosquito survival. Moreover, the diseases themselves have an intrinsic intra-annual cycle in which the proportion of a given population that is susceptible to infection fluctuates between years, confounding the climate-driven associations with temperature and precipitation. 

That leaves us with a dissatisfying ‘we don’t know’ and ‘it all depends.’ Our experience will depend on the previous years’ mosquito abundance, previous years’ human or other host disease occurrence, current human or other host susceptibility, and the duration of the anomalous weather. It does leave us with a positive message, though: what we do as individuals does matter. Protect yourself from mosquitoes, empty breeding sites, cover your water storage, repair your window screens, and use mosquito repellent when you go out of doors. 

El Niño Tracker - Nov 2015

Saturday, November 21, 2015

Originally published as part of the Nov 2015 CLIMAS Southwest Climate Outlook

El Niño conditions continued for a ninth straight month, and models continue to forecast a strong El Niño event that likely will last through spring 2016 and remain strong through the early part of the year. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1–2) and weakened trade winds, enhanced convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling.

Image Source - Australian Bureau of Meteorology

Image Source - NOAA/NWS - Climate Prediction Center

On Nov 10, 2015, the Japan Meteorological Agency identified ongoing El Niño conditions in the equatorial Pacific, and in particular “remarkably above normal” SST anomalies and atmospheric convective activity, with projections that El Niño would remain in place through spring 2016. On Nov 10, 2015, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, remarking on the persistent strength of oceanic and atmospheric indicators. On Nov 12, 2015, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, and identified the current atmospheric and oceanic anomalies as reflecting “a strong and mature El Niño episode”.  Their models indicate the El Niño event will persist through winter, with a transition to ENSO neutral conditions by late spring or early summer. On Nov 19, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated that both sea surface temperature anomalies and atmospheric variables were indicative of a strong El Niño event, with consensus centering on strong El Niño conditions that might strengthen even more into early winter 2015-2016, before gradual weakening into spring 2016 (Fig. 3). 

Image Source - International Research Institute for Climate & Society

The North American multi-model ensemble currently shows a strong event extending into 2016 with gradual weakening heading into spring (Fig. 4). The ocean and atmosphere are indicative of a strong El Niño event that shows no sign of weakening, and current forecasts that have it pegged as one of the strongest events on record.  There is little doubt that El Niño will remain on the current trajectory in the near term, and we will see one of the top three strongest events on record since 1950.

Image Source - NOAA/NWS - Climate Prediction Center

What does this mean for the Southwest? Seasonal forecasts and past events suggest we should see well above-average cumulative precipitation totals over the cool season.  We should not expect a winter of daily rains, however, as there will likely be periods of inactivity between storms.  Looking at the 1997–1998 event—the strongest El Niño event on record—most of Arizona and New Mexico received above-average precipitation in December but below-normal precipitation for all of January before returning to normal or above-normal precipitation in February and March (Figs. 5–8).

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

In order to track this variability and provide data and analysis regarding possible impacts of El Niño on the Southwest, CLIMAS has created an El Niño hub. This is our repository for news and information about the expected impacts of El Niño, from the perspective of what is most relevant and applicable to the Southwest. This includes what we have learned from past El Niño events, and what forecasting and models can tell us about planning for the ongoing event.

Notes from an Applied Climatologist: How does El Niño affect the monsoon in the Southwest?

Sunday, October 18, 2015

Research on the interactions between El Niño events and the North American Monsoon System suggests that during past El Niño events, there was a slowing of the onset of monsoon precipitation across the Southwest U.S.  

In summer 2014 the monsoon moved in right on time, ushered in by surges of moisture that moved up the Gulf of California into the desert Southwest, several of which were triggered by tropical storms and hurricanes in the eastern Pacific that flourished in highly favorable conditions, including light upper level winds and very warm ocean water.  These conditions were not necessarily related to El Niño, as conditions that favor an El Niño event were largely absent in the atmosphere, with only glimmers of favorable patterns of sea surface temperatures across the eastern Pacific Ocean, and the fact that the current El Niño had been struggling to form (in 2014) may be one reason we had a relatively "normal" start to the monsoon (in 2014)

In summer 2015, monsoon moisture moved in ahead of schedule in late June with dewpoints in southern Arizona skyrocketing from the low 30’s (F) in mid-June to above 60F by the end of the month. Abundant tropical moisture was drawn north up into the Southwest as the subtropical ridge expanded and strengthened over the western U.S. Previous research on connections between monsoon onset and El Nino suggest that during strong El Nino events, the subtropical ridge struggles to form early on and delays the onset of the season. This was not the case this year as a moderate to strong El Nino was fully engaged with the atmospheric circulation pattern across the globe. It is possible that strong Madden-Julian Oscillation activity through June helped offset some of the typical ENSO effects on the North American Monsoon early on in the season.


For more on this year's monsoon, see the monsoon recap in the Oct 2015 CLIMAS SW Climate Outlook

El Niño Tracker - Oct 2015

Thursday, October 15, 2015

Originally published in the Oct 2015 CLIMAS Southwest Climate Outlook

We spent the better part of 2014 (and the first part of 2015) waiting in anticipation for an El Niño event that was initially forecast to be one of the stronger events on record. By early 2015, the event in question had not yet materialized, and some questioned whether El Niño would ever arrive. Eventually it did, and has been going strong for months, with most forecasts indicating that it will remain a strong event through the winter. As this event unfolds, there are numerous impacts we might expect to see across the Southwest over the course of our cool season (approximately Oct - Mar). In the coming months, CLIMAS will aggregate news, information, and commentary about the possible and expected impacts of El Niño, from the perspective of what is most relevant and applicable to the Southwest. This will include what we have learned from past events, and what forecasting and models can tell us about planning for this event.

For more information, please visit our repository for ENSO related materials, which we will update with timely and relevant information about El Niño throughout the winter.


2015 El Niño Tracker

El Niño conditions continued for an eighth straight month, and models continue to forecast a strong El Niño event that likely will last through spring 2016 and remain strong through the early part of the year. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1–2) and weakened trade winds, enhanced convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling.

Image Source - Australian Bureau of Meteorology

Image Source - NOAA/NWS - Climate Prediction Center

On October 8, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, predicting a 95 percent chance that the current strong El Niño conditions will continue through winter 2015–2016, with gradual weakening into spring 2016 (Fig. 3). The center cited persistent positive SST anomalies in the central and eastern Pacific and ongoing ocean-atmospheric coupling and convection activity as indicators of an ongoing and strengthening event. On October 9, the Japan Meteorological Agency identified ongoing El Niño conditions in the equatorial Pacific, noting “remarkably above-normal” SST anomalies and convective activity, and forecast the current El Niño conditions would continue into spring. On October 13, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, noting the strongest event seen since 1997, and forecast the event will persist into early 2016. On October 15, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated a 100 percent chance of El Niño through early 2016, and saw continued evidence in both the ocean and atmosphere that this event would be one of the strongest events on record.

Image Source - International Research Institute for Climate & Society

The North American multi-model ensemble currently shows a strong event extending into 2016 with gradual weakening heading into spring (Fig. 4). We continue to grapple with this El Niño event and the potential impacts it might bring to the Southwest over the winter and into spring, especially given current forecasts that have it pegged as one of the strongest events on record. Seasonal forecasts (see Fig. 5 on Maps Page) and past events suggest we might expect well above-average precipitation totals across our cool season. This does not mean we should expect a winter of daily rains, however. Variability across these months means we may see periods of below-average precipitation as well. 

Image Source - NOAA/NWS - Climate Prediction Center

Looking at the 1997–1998 event—the strongest El Niño event on record—most of Arizona and New Mexico received above-average precipitation in December but below-normal precipitation for all of January before returning to normal or above-normal precipitation in February and March (Figs. 5–8). At this point, we are fairly certain that El Niño will remain on the current trajectory, and we will see one of the top three strongest events on record since 1950. This is likely to bring above-average winter precipitation to the Southwest, particularly later in the season, but it is far from a guarantee. Additionally, what happens in late spring and early summer may determine the longer-term impacts. If we bounce back into La Niña conditions, as happened after the 1997–1998 event, we may see a return to more below-average precipitation forecasts heading into 2016–2017. 

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

Image Source - Western Regional Climate Center - WestWide Drought Tracker

El Niño is here…what exactly does that mean for Arizona and New Mexico?

Thursday, September 24, 2015

“El Niño” has been all over the news lately, even garnering comparisons to a Godzilla – a prehistoric sea monster awakened and empowered by nuclear radiation (thank you Wikipedia). This characterization is in response to the near record strength of this El Niño event, which is exciting for climate enthusiasts, but leaves most people wondering; what does a strong El Niño event actually mean for Arizona and New Mexico? Are we talking floods? Droughts?  Plagues of locusts? Additionally, how soon can we expect this “El Niño” character to show up?  In other words, what does a realistic assessment look like?

First of all, El Niño is not a singular weather event that will storm ashore on a particular date.  Climate.gov has come up with an excellent analogy – tying the effects of El Niño to a big construction project - you will definitely feel the effects, but these vary with space and time and are dependent on a number of factors. There are a number of El Niño primers (e.g. the climate.gov ENSO blog) that explain how El Niño works in technical terms, but to put it simply, El Niño is part of the El Niño-Southern Oscillation (ENSO) which is a semi-regular shift on the order of several years (Figure 1, Oceanic Niño Index) in sea surface temperatures, atmospheric pressure, and rainfall patterns, along the equator in the Pacific Ocean. These shifts (between El Niño and La Niña event) reorganize global weather patterns that can drive drought and flood patterns on a regional basis.

Our understanding of the global impact of El Niño events has improved considerably over the last few decades. In particular, we can often detect the development of an El Niño event months in advance, long before it will ever have an impact on seasonal weather conditions.  For Arizona and New Mexico, an El Niño event means increased probability of receiving above-average winter precipitation, generally between October and March. However, there is still plenty of variability when comparing El Niño events, and there is no guarantee that any given El Niño event will lead to wetter than average conditions.

In order to look more closely at this relationship, it helps to take a look at plots describing the relationship between past El Niño and La Niña events, and October-March total precipitation for select regions in Arizona and New Mexico.[1] A couple key points:

  1. We will be looking at precipitation totals within climate divisions, which represent average values over large multi-county areas (Figure 2, AZ & NM Climate Divisions).  These totals are calculated using station observations within these regions. 
  2. We will be using a simple metric called the Oceanic Nino Index (ONI) to assess the phase and strength of ENSO. The ONI describes temperature anomalies (warm or cool) in the central and eastern Pacific Ocean along the equator, which in turn relates to shifts in tropical thunderstorm activity and resultant impacts to global atmospheric circulation

Figures 3a & 3b compare the ENSO-precipitation relationship for two regions in Arizona (climate division 3 and climate division 7).  Total cool-season precipitation is on the y axis, and the average ONI value for the same Oct-March period is on the x axis. The dots are color coded: red to reflect El Niño events (ONI values > 0.5), blue for La Niña events (ONI values < -0.5), and green for ENSO neutral years (ONI between -0.5 and 0.5).. At first glance, the blue dots (La Niña years) are clustered much lower on the y-axis, while the red dots (El Niño years) are much higher on this axis.  This characterizes the historical connection between La Niña events and dry winters, while El Niño years are associated with wet winters. The horizontal lines on the plots are the average cool-season precipitation for all years (black line), La Niña years (blue line), and El Niño years (red line), and help illustrate this relationship further. 

The more you stare at this graph (trust me, we’ve done our share of staring!), the more you see that this relationship is complicated, and even varies between the two regions in Arizona. In general there is a relationship between the ONI index value and the amount of cool-season precipitation (see correlation values on each figure), but this relationship is noisy at best, and demonstrates that the strength of the ENSO phase (in this case using ONI) isn’t a perfect linear fit with total cool season precipitation. Some of the biggest outliers are linked to weak or even moderate strength El Niño events, but are associated with below average winter precipitation (We're looking at you, 2007).  This is especially evident as you move north in the region (see climate division #3), where the relationship between El Niño strength and cool season precipitation is even weaker. What’s the point of all this?  El Niño is not a slam dunk forecast for unusually wet cool season conditions for the Southwest.

But…this year we are in rare territory with respect to the current and forecasted strength of this El Niño event. Current forecast models indicate that ONI values should reach approximately 2 deg C (above normal) over the upcoming winter season, making it one of the strongest El Niño events on record and on par with past big events like 1982-83 and 1997-98. When we look for these years on the plots in figure 2, we see that both of these years were associated with above-average precipitation.  In fact, the three “strong” events (1973, 1983, 1998) and the as well as the five “moderate” years (1958, 1966, 1987, 1992, 2010) all saw above average precipitation, which means that as long as this event stays strong (all indications are that it will) we will likely see a wetter than average winter.  A large caveat being the sample size of this relationship is VERY small.  

This pattern is even stronger for climate division 7 (southern Arizona) where the overall relationship between ONI and cool season precipitation is stronger. This is consistent with observations that the relationship between ENSO and winter precipitation is stronger over southern parts of Arizona (Figure 4, Percent of normal winter precipitation 1983 & 1998) and New Mexico. This can be attributed to a stronger than average and more persistent sub-tropical jet stream that favors southern Arizona and New Mexico with above-average winter storm activity. 

The current seasonal precipitation forecasts for the upcoming winter season issued by the NOAA Climate Prediction Center also reflect this expectation for additional moisture, especially in the SW. The best chances for observing above-average winter precipitation cover all of Arizona and New Mexico, but are slightly better for the southern half of each state. There is a pretty good chance that the next red dot for this upcoming year that shows up on these plots will be above-average for most climate divisions across the Southwest, but how much above-average will be very interesting to see.


[1] We are borrowing this idea from the Western Regional Climate Center.

El Niño Tracker - September 2015

Friday, September 18, 2015

El Niño conditions continued for a seventh straight month, and forecasts and models indicate this event likely will last through spring 2016, remaining strong through the early part of the year. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1–2) and weakened trade winds, ongoing convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling.

On September 10, the Japan Meteorological Agency identified persistent El Niño conditions in the equatorial Pacific, especially SST anomalies and convective activity, and forecast that the current El Niño conditions were likely to persist through winter. That same day, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, predicting a 95 percent chance that El Niño will continue through winter 2015–2016, with gradual weakening into spring 2016 (Fig. 3). The center cited persistent positive SST anomalies in the central and eastern Pacific and ongoing ocean-atmospheric coupling and convection activity as indicators of an ongoing and strengthening event. On September 15, the Australian Bureau of Meteorology maintained its tracker at official El Niño status; a strong event with the potential to exceed the 1997–1998 El Niño in strength. On September 17, the International Research Institute for Climate and Society (IRI) and CPC forecasts corroborated the forecast of a strong El Niño with the potential to rival the strongest events on record.

The North American multi-model ensemble currently shows a strong event extending into 2016 (Fig. 4). Emergent questions have centered on how this event compares to other strong events such as those in 1982–83 and 1997–98. If El Niño remains on this trajectory, it will likely be one of the top three strongest events on record since 1950. Sensationalistic media coverage already has started but it will be important to temper expectations without minimizing possible impacts. Forecast consensus is for a strong El Niño that extends into winter 2015–2016 and would likely bring above-average winter precipitation in the Southwest, particularly later in the season. It is important to note that this relationship suggests that a strong El Niño event gives the Southwest a much better chance at increased precipitation totals by March or April, but it is far from a guarantee of increased precipitation. In the more immediate future, El Niño conditions could lead to a repeat of 2014’s above-average eastern Pacific tropical storm season, when conditions favorable to El Niño were thought to be driving increased tropical storm activity in the Southwest in September and October.

Southwest Climate Outlook September 2015

Thursday, September 17, 2015

Precipitation:  In the past 30 days, much of Arizona and New Mexico recorded below-average precipitation, although isolated areas received above-average precipitation (Fig. 1). This is consistent with the variable nature of the monsoon, especially during the seasonal transition. Water year precipitation to date (since Oct 1, 2014) offers hope in terms of drought relief, with much of Arizona and New Mexico recording above-average precipitation for the water year (Fig. 2).

Temperature: Temperature anomalies in the past 30 days were between 0 and 6 degrees F above average across most of Arizona and New Mexico (Fig. 3). Despite similarly near-record warm temperatures so far in 2015, temperatures have not felt as hot as they did last year, with above-average humidity suppressing daytime high temperatures and boosting nighttime lows. Arizona recorded near-record high statewide average temperatures from January to August 2015, while average temperatures in New Mexico for the same time period were among the state’s top 10 warmest (Fig. 4). Extremely hot days have been rare, with fewer than average very hot days across the region.

Monsoon: Variable spatial coverage and intensity along with intermittent frequency of precipitation events makes it difficult to characterize any monsoon as “normal.” That said, 2015 has been fairly typical for monsoon precipitation; the storms have been variable, most locations saw regular precipitation events that brought their total precipitation close to long-term averages, and, unlike last year, fewer locations recorded high-intensity precipitation events that dropped a full season or years’ worth of precipitation in a single storm event (see Monsoon Tracker on pgs. 6-7 for details).

Tropical Storm Activity: During late summer and into fall, tropical storms in the eastern Pacific Ocean have a better chance to recurve back into the Southwest, rather than heading west across the Pacific Ocean. Record sea surface temperatures intensify these storms, upping the chance that an organized system will bring moisture (humidity) and precipitation to the Southwest. Despite regular incursions of tropical moisture, we have not seen many heavy precipitation events associated with tropical storms, as we did with Norbert and Odile in 2014, save for recent extreme flooding in northern Arizona and Utah. However, we are just past the midway point of the tropical storm season, leaving time for tropical storm systems to bring additional (possibly heavy) rainfall to the region.

Drought & Water Supply: The U.S. Drought Monitor identifies persistent multi-year drought across the West. Arizona and New Mexico are grappling with years of accumulated drought and water deficits, but water year precipitation has helped scale back drought conditions, particularly in New Mexico (see Reservoir Volumes on pg. 8 for details).

Precipitation & Temperature Forecasts: The Sept. 17 NOAA-Climate Prediction Center seasonal outlook predicts above-average precipitation for most of the Southwest this fall (Fig. 5, top). Notable exceptions are northern California and most of the Northwest. Temperature forecasts are split, with elevated chances for above-average temperatures along the West Coast and into southwestern Arizona, and increased chances for below-average temperatures centered over Texas and extending across most of New Mexico (Fig. 5, bottom).

El Niño Tracker - August 2015

Friday, August 21, 2015

Originally published in the August 2015 CLIMAS Southwest Climate Outlook

El Niño conditions continued for a sixth straight month and forecasts and the most recent outlooks offer a consistent cluster of forecasts calling for a clear El Niño signal similar to past strong events, lasting into early 2016. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1–2) and on weakened trade winds, ongoing convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling.

Image Source - Australian Bureau of Meteorology

Image Source - National Climatic Data Center

On August 10, the Japan Meteorological Agency identified persistent El Niño conditions in the equatorial Pacific, especially SST anomalies and convective activity, and forecast that the current El Niño conditions were likely to persist until winter. On August 13, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, predicting more than a 90-percent chance that El Niño will continue through winter 2015–2016 and an 85-percent chance it will last into early spring 2016 (Fig. 3). The center cited persistent positive SST anomalies in the central and eastern Pacific and ongoing ocean-atmospheric coupling and convection activity as indicators of an ongoing and strengthening event. On August 18, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, identifying a strengthening El Niño with strong ocean-atmosphere coupling and projecting the event is likely to persist into 2016. On August 20, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated the persistence of strong El Niño conditions, with possible further strengthening during fall 2015, and extending well into spring 2016. The North American multi-model ensemble currently shows a strong event extending into 2016 (Fig. 4).

Image Source - International Research Institute for Climate and Society

Image Source - NOAA - Climate Prediction Center

Given that the current and projected strength of the El Niño is strong with no sign of weakening, emergent questions have centered on how this event compares to other strong events such as those in 1982–83 and 1997–98. Limited data makes comparisons and statistical analyses more difficult, and each event has a unique context that affects its impact. If El Niño remains on this trajectory, it most likely will be one of the top three or four strongest events on record since 1950, with implications for both Southwest and global communities. Sensationalistic media coverage already has begun (see recent coverage of “Godzilla” El Niño), but it will be important to temper expectations without minimizing possible impacts. 

The general consensus is that a strong El Niño extending into winter 2015–2016 would likely bring above-average winter precipitation in the Southwest (Fig. 5), particularly later in the season. It is important to note that this relationship suggests that a strong El Niño event gives the Southwest a much better chance at increased precipitation totals by March or April, but it is far from a guarantee of increased precipitation. Current CPC forecsts do indicate increased an chance of precipitation in late fall and early winter, but the region could very well see a relatively dry period through early 2016 following the close of the eastern Pacific tropical storm season; this would not necessarily mean that El Niño was a “bust.” In the more immediate future, El Niño conditions could lead to a repeat of 2014’s above-average eastern Pacific tropical storm season, when conditions favorable to El Niño were thought to be driving increased tropical storm activity in the Southwest in September and October.

Image Source - NOAA Climate.gov

El Niño Tracker - July 2015

Monday, July 20, 2015

El Niño conditions continue for a fifth straight month, and at this point, forecasters are relatively bullish that we are witnessing the development of a moderate-to-strong event that could rival 1997 in absolute magnitude later this year. The most recent outlooks from various sources offer a consistent cluster of forecasts calling for a clear El Niño signal that is maintained or even strengthens well into early 2016. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1 - 2) along with weakening trade winds, ongoing convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling.

On July 7, the Australian Bureau of Meteorology maintained its tracker at official “El Niño” status, identifying a strengthening El Niño (in part due to increased tropical storm activity), and projecting the event as likely to persist through the end of 2015 and into 2016. On July 10, the Japan Meteorological Agency identified strengthening El Niño conditions in the equatorial Pacific, and forecast that the current El Niño conditions were likely to last until winter. On July 9, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory with a greater than 90-percent chance that El Niño will continue through winter 2015-2016, and an 80-percent chance it will last into early spring 2016. It cited the increasingly positive SST anomalies in the central and eastern Pacific and ongoing ocean-atmospheric coupling and convection activity as indicators of an ongoing and strengthening event (Fig. 3). On July 16, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated continued strengthening of El Niño through 2015 and into 2016, with a moderate event likely becoming a strong event by summer or early fall and lasting into early 2016. The North American multi-model ensemble currently shows a moderate event extending through early summer, with potential for a strong event by mid-summer or early fall (Fig. 4).

It is clear that we are in the midst of an ongoing and strengthening El Niño event.  If this event remains on the current trajectory, it could surpass the strongest El Niño events of recent decades (1997 in particular), with implications for both Southwest and global communities. 

In May and early June, we witnessed exactly the sort of patterns we might expect to see in Arizona and New Mexico under El Niño conditions—above-average precipitation and below-average temperatures. If El Niño persists into winter 2015-2016, particularly if it remains a moderate-to-strong event, we would likely continue to see above-average precipitation in the Southwest (Fig. 5). Although the presence of El Niño conditions often has been associated with a delay in the start of the monsoon, this year the monsoon began early. However, a resurgent El Niño signal now may be pushing back and could work to disrupt the monsoon ridge, leading to one or more ‘breaks’ in the monsoon. The event could also lead to a repeat of 2014’s above-average eastern Pacific tropical storm season, when conditions favorable to El Niño were thought to be driving increased tropical storm activity in the Southwest in September and October.

Image Source - Australian Bureau of Meteorology

Image Source - National Climatic Data Center

Image Source - International Research Institute for Climate and Society

Image Source - NOAA - Climate Prediction Center

Image Source - NOAA Climate.gov

El Niño Tracker - June 2015

Friday, June 19, 2015

Originally Published in the June 2015 CLIMAS SW Climate Outlook (SWCO)


El Niño conditions continued for a fourth straight month with no signs of weakening or disorganizing. Forecasts focused on the persistence of sea-surface temperature (SST) anomalies (Figs.1 - 2) along with weakening trade winds, ongoing convective activity, and El Niño-related ocean-atmosphere coupling. Despite the high degree of uncertainty associated with forecasting El Niño this time of year (the so-called spring predictability barrier), the most recent outlooks from various sources offer a consistent cluster of forecasts calling for a clear El Niño signal that is maintained or even strengthening. 


Image Source - Australian Bureau of Meteorology


Image Source - National Climatic Data Center

On June 9, the Australian Bureau of Meteorology maintained its tracker at official “El Niño” status, identifying persistent SST anomalies, weak trade winds, and ocean-atmospheric coupling as indicators this El Niño event was strong enough to extend through 2015. On June 10, the Japan Meteorological Agency identified strengthening El Niño conditions in the equatorial Pacific, and forecast that the current El Niño conditions were likely to last until winter. On June 11, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory with a 90 percent chance that El Niño will continue through fall 2015 and an 85 percent chance the event would last through winter 2015-2016.  It pointed to the increasingly positive SST anomalies, along with ongoing ocean-atmospheric coupling and dateline convection activity, as indicators of an ongoing and strengthening El Niño event (Fig. 3). On June 18, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated continued strengthening of El Niño through 2015, with a moderate event during summer and likely stronger in the fall, lasting into early 2016. The North American multi-model ensemble currently shows a moderate event extending through early summer, with potential for a strong event by mid-summer or early fall (Fig. 4).


Image Source - International Research Institute for Climate and Society


Image Source - NOAA - Climate Prediction Center

Last year’s vacillating signals and forecasts may have led forecasters to take a more conservative approach when presented with similar conditions earlier this year to avoid repeating the “enthusiastic” forecasts of Spring 2014 that didn’t immediately pan out.  That said, we appear to be in the midst of an ongoing and strengthening El Niño event.  If this event remains on the current trajectory, it could rival our strongest El Niño events of recent memory (1997 in particular), with implications for both Southwest and global communities.

The recent above-average precipitation and below-average temperatures in Arizona and New Mexico are exactly the sort of patterns we expect to see under El Niño conditions. In the immediate future, we may see a return of some early season tropical storm activity, as we did with Hurricane Blanca in June. El Niño also points toward a possible delay in the start of the monsoon, which could actually extend the hotter and drier early portion of summer. We could also see a repeat of 2014’s above-average eastern Pacific tropical storm season, when conditions favorable to El Niño were thought to be driving increased late-season tropical storm activity in the Southwest.  And if El Niño persists into winter 2015-2016, particularly if it remains a moderate-to-strong event, we would likely see patterns of above-average precipitation in the Southwest (Fig. 5).


Image Source - NOAA Climate.gov

El Niño Models - May 2015 SW Climate Podcast

Friday, June 19, 2015

Excerpt from the May 2015 CLIMAS SW Climate Podcast


Image & Story Credits

The Jetstream & El Niño - Looking back at 2014-2015, and forward to 2015-2016

Wednesday, May 27, 2015

Excerpt from the May 2015 Southwest Climate Podcast


Image & Story Credits

2015 El Niño Tracker

Friday, May 22, 2015

Originally published in the May 2015 CLIMAS SW Climate Outlook


El Niño continued for a third straight month, with no signs of weakening or dissipating. Forecasts keyed in on persistent sea surface temperature (SST) anomalies (Figs. 1–2), along with weakening trade winds, ongoing convective activity, and El Niño-related ocean-atmosphere coupling. If these conditions continue, we are likely to see the effects of a moderate El Niño event–or stronger if conditions continue to strengthen. Spring forecasts have a higher degree of uncertainty, owing to the so-called spring predictability barrier, a likely source of vacillations in recent forecasts. 

Image Source - Australian Bureau of Meteorology

Image Source - NOAA-National Climatic Data Center

Current forecasts offer a consistent and bullish forecast compared to last month, when they were integrating mixed signals regarding the strength of El Niño. On May 12, the Japan Meteorological Agency reversed course with an observation that strengthening El Niño conditions in the equatorial Pacific reflected an ongoing El Niño event that was likely to last through at least fall 2015. On May 12, the Australian Bureau of Meteorology upgraded its tracker to official El Niño status, identifying persistent SST anomalies, weak trade winds, and increasing ocean-atmospheric coupling serving as indicators this El Niño event was strong enough to extend into 2015. On May 14, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory with a 90 percent chance that El Niño will continue through summer 2015 and an 80 percent chance the event will last through 2015 (Fig. 3). The CPC pointed to positive SST anomalies, along with ongoing ocean-atmospheric coupling and dateline convection activity, as indicators of a weak to moderate El Niño event that will likely continue for most of 2015. On May 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts confirmed we are in the midst of an El Niño event that appears to be strengthening, with the current forecast suggesting a moderate to strong El Niño event persisting into 2016. The North American multi-model ensemble shows a moderate event extending through the spring, with potential for a strong event by summer or early fall (Fig. 4).

Image Source - International Research Institute for Climate and Society

Image Source - NOAA-Climate Prediction Center

After a series of fits and starts, the pieces finally seem in place for the El Niño event forecasters expected to start last year. This is partially evidenced by the recent above-average precipitation and below-average temperatures in Arizona and New Mexico in late April and early May—exactly the sort of springtime weather we might expect to see if El Niño conditions were present and affecting our weather patterns. If the event persists into fall and winter 2015, and particularly if it remains a moderate to strong event, we will likely see patterns of above-average precipitation in the Southwest. There is also the possibility of a repeat of the 2014 tropical storm season, in which conditions favorable to El Niño were thought to have driven the increased tropical storm activity in the Southwest. 

El Niño Tracker - April 2015

Friday, April 17, 2015

This was originally published in the April 2015 Southwest Climate Outlook


Strong signals in early 2014 stalled, delaying El Niño’s onset until last month, when ocean-atmosphere coupling and an additional Kelvin wave indicated more favorable conditions. Despite this late start, El Niño continued for a second consecutive month. Recent increases in sea surface temperature (SST) anomalies (Fig.1 - 2) and ongoing convective activity associated with El Niño-favorable conditions indicate we might be witnessing a two-year El Niño event. These forecasts rely on projections during a time of increasing uncertainty, and the so-called “spring predictability barrier” continues to make it difficult to anticipate how seasonal changes will help or hinder El Niño. 

Image Source - Australian Bureau of Meteorology

Image Source - NOAA-National Climatic Data Center

The most recent forecasts continue to offer mixed signals regarding El Niño, but are more bullish this spring than last year. On April 9, the NOAA-Climate Prediction Center (CPC) issued an El Niño advisory with a 70 percent chance that El Niño will continue through summer 2015 and more than a 60 percent chance the event would last through fall.  They pointed to the large Kelvin wave, along with ongoing ocean-atmospheric coupling, as an indication a weak El Niño event would linger, with potential for further development in the long term. On April 10, the Japan Meteorological Agency declared the El Niño event likely to have ended in winter 2015, with current conditions being ENSO-neutral, but also projected El Niño conditions could return by summer.  On April 14, the Australian Bureau of Meteorology upgraded their tracker to “alert” status (one below an official El Niño designation), with warming in the tropical Pacific, weak trade winds, and projected additional ocean warming listed as contributing factors. On April 16, the International Research Institute for Climate and Society (IRI) and CPC forecasts highlighted increasingly favorable oceanic and atmospheric conditions, with an 80 percent probability of El Niño extending from summer into fall, and a 70 percent probability of El Niño extending into next winter (Fig. 3).  The North American multi-model ensemble shows a weak event extending through the spring, with potential for a moderate or even strong event by summer or early fall (Fig. 4).

Image Source - International Research Institute for Climate and Society

Image Source - NOAA-Climate Prediction Center

This El Niño event continues to defy expectations, with some models indicating conditions are strengthening rather than weakening during the spring transition.  Forecasting or characterizing this event remains difficult given the lack of analog events in the historical record, and the complexity of this El Niño guarantees it will be of interest to climatologists for years to come. Seasonal forecasts continue to indicate an increased chance of above-average precipitation through much of the Southwest, likely tied to the presence of El Niño favorable conditions. Perhaps more interesting is the possibility of a repeat of 2014’s tropical storm season, when conditions favorable to El Niño were thought to have been driving increased storm activity in the Southwest.

El Niño Tracker - March 2015

Friday, March 20, 2015

Originally published Mar 19, 2015 in the CLIMAS Southwest Climate Outlook

After months of vacillating sea surface temperature (SST) anomalies, limited coordination between oceanic and atmospheric conditions favorable to El Niño formation, and ongoing confusion regarding the strength of the various diagnostic signals, El Niño has “officially” arrived in North America. This is late in the season to declare an El Niño, and the so-called spring predictability barrier makes it difficult to anticipate how seasonal changes, particularly westerly wind bursts, will help or hinder the ongoing conditions favorable to El Niño. This has been a strange season.  Strong signals in early 2014 stalled in summer and into fall, delaying the event’s onset until this month, when ocean-atmosphere coupling and an additional Kelvin wave again indicated more favorable conditions for an El Niño event.

The most recent forecasts offer mixed signals regarding El Niño. On Mar. 5, the NOAA-Climate Prediction Center (CPC) issued an El Niño advisory, maintaining a 50–60 percent probability of a weak El Niño event developing and extending through the summer. On Mar. 10, the Japan Meteorological Agency declared the El Niño event likely to have ended, with greater likelihood of a return to El Niño than ENSO neutral conditions in the summer. On Mar. 17, the Australian Bureau of Meteorology elevated its El Niño tracker from neutral back to watch status, noting the “unusual conditions” in the tropical Pacific, including warmer-than-average SST anomalies (Fig. 1-2). On Mar. 19, the International Research Institute for Climate and Society (IRI) and CPC reasserted a 50–60 percent probability of this El Niño event extending into summer 2015 (Fig. 3), similarly noting atypical (or even strange) conditions that have made characterizing this particular event difficult.  The North American multi-model ensemble shows a weak event extending into summer (Fig. 4), and corroborates the forecast discussion that suggests an increased possibility of a stronger El Niño signal extending into 2016.  While the models are bullish on the possibility of a moderate to strong event, this will depend on how ocean and atmospheric conditions progress from summer into fall. 

With a seemingly definitive El Niño declaration, we are finally out of “El Limbo”.  While forecasting or characterizing this event has been difficult for all involved, the complexity of this El Niño will be of interest to climatologists for years to come.  Looking forward, seasonal forecasts still indicate an increased chance of above-average precipitation through much of the Southwest for late winter and spring. Despite numerous storm events, we have yet to see widespread and sustained above-average winter precipitation in the Southwest, which would help considerably in mitigating longer-term drought conditions.

Image Source - Australian Bureau of Meteorology

Image Source - NOAA-National Climatic Data Center

Image Source - International Research Institute for Climate and Society

Image Source - NOAA-Climate Prediction Center

El Niño Tracker - Southwest Climate Outlook February 2015

Friday, February 20, 2015

Originally published in the Feb 2015 CLIMAS Southwest Climate Outlook

2014-15 El Niño Tracker

A definitive 2014–2015 El Niño forecast remains elusive. Weak El Niño conditions have continued in 2015, but recent backsliding in SST anomalies (Fig. 1), especially in the Niño 1-2 regions (Fig. 2), along with the ongoing lack of coordination between atmospheric and oceanic conditions, give little confidence that the 2014–2015 event will be characterized as anything more than a weak El Niño.

Image Source - Australian Bureau of Meteorology

Image Source - NOAA-National Climatic Data Center

The most recent forecasts dialed back the probabilities for El Niño this winter and spring, and hinted we could swing to ENSO-neutral by late spring. On Feb. 5, the NOAA-Climate Prediction Center (CPC) issued another El Niño Watch, maintaining a 50–60 percent probability of an El Niño event, most likely a weak event extending into late winter or early spring. On Feb. 10, the Japan Meteorological Agency continued its assessment that El Niño conditions had been present in the equatorial Pacific for multiple months. They noted uncertainty as to the length or intensity of an El Niño event, with emphasis on a weak event that would transition to ENSO-neutral by early spring. On Feb. 17, the Australian Bureau of Meteorology kept its El Niño tracker status at neutral, given the fade in SST anomalies and lack of clear atmospheric signal. On Feb. 19, the International Research Institute for Climate and Society (IRI) and CPC reasserted a 50–60 percent probability of an El Niño event (Fig. 3).  Given the declining SST anomalies and lack of clear atmospheric signal, they characterized this event as a “borderline El Niño” that would last through early spring 2015. The North American multi-model ensemble shows a weak event that extends into summer (Fig. 4). This graph highlights the possibility of a continuation of a stronger El Niño signal into 2015 (a possibility that was discussed in the IRI-CPC forecast event), depending on how ocean and atmospheric conditions progress from summer into fall.  The dynamical models currently favor a resurgence of El Niño conditions, while the statistical models suggest an ENSO-neutral state.

As with last month, we remain in “El Limbo” with seasonal forecasts still indicating an increased chance of above-average precipitation across the Southwest for winter and early spring. These forecasts are linked to the projected influence of El Niño conditions, but impacts associated with weak El Niño events are less certain than those associated with moderate or strong events (past weak events have brought both dry and wet conditions to the Southwest during the winter). A number of storm events have moved through the Southwest in late 2014 and early 2015, but conditions have not converged to produce widespread above-average precipitation over an extended period of time.  For this El Niño event to be of some utility in mitigating longer-term drought conditions, we would hope to see this convergence this winter into spring, with more widespread and sustained precipitation events.

Image Source - International Research Institute for Climate and Society

Image Source - NOAA-Climate Prediction Center

El Niño Tracker - January 2015

Friday, January 23, 2015

Originally published in the January 2015 Southwest Climate Outlook (SWCO)

Just when it looked like we were getting a more definitive answer regarding El Niño, ongoing lack of cooperation on the part of the atmosphere continues to muddy forecasts moving into 2015. Sea surface temperatures (SSTs) remain elevated across much of the equatorial Pacific Ocean (Fig. 1), and while temperature anomalies in the Niño 3.4 region are within the range of a weak El Niño event, they have declined in the past month (Fig. 2). It is a common refrain in forecast bulletins that a lack of coupling between ocean and atmosphere is responsible for decreased confidence in an El Niño event this winter. Additionally, a lack of temperature gradient along the equatorial Pacific and little in the way of El Niño wind patterns further reduce confidence that a stronger event is on the horizon.

Source: Australian Bureau of Meteorology

Source: NOAA-National Climatic Data Center

The most recent forecasts remain in a cautious holding pattern, pending the emergence of a more decisive signal. On Jan. 8, the NOAA-Climate Prediction Center (CPC) issued another El Niño Watch, assigning a 50 to 60 percent probability that an El Niño would form in the next two months, with forecaster consensus that this would be a weak event extending into late winter or early spring. On Jan. 9, the Japan Meteorological Agency continued its assessment that El Niño conditions had been present in the equatorial Pacific for multiple months but noted uncertainty as to the length or intensity of an El Niño event, with emphasis on a weak event that would transition to ENSO-neutral by early spring. On Jan. 15, the International Research Institute for Climate and Society (IRI) and CPC scaled back the probability of an El Niño formation to approximately 60 percent (Fig. 3) but indicated SST anomalies were sufficient enough to suggest a weak El Niño event was likely underway and would last through spring 2015. On Jan. 20, the Australian Bureau of Meteorology actually shifted its El Niño tracker status to neutral, given the fade in SST anomalies and lack of clear atmospheric signal. The North American multi-model ensemble shows a weak event that extends into summer (Fig. 4). 

Source: International Research Institute for Climate and Society

Source: NOAA-Climate Prediction Center

Vacillations in forecast percentages prompted the forecast community to describe current conditions as “El Limbo.” Despite lack of official status, El Niño-like conditions may already be driving winter patterns, and seasonal precipitation forecasts indicate an enhanced chance for above-average precipitation this winter across the Southwest, although confidence in this forecast is partially contingent on the strength of these El Niño conditions. Impacts associated with weak El Niño events are generally less certain than those of a moderate or strong event, with past weak events bringing both dry and wet conditions to the Southwest U.S. during the winter. Ultimately, the above-average tropical storm season and the humidity that remained in the region may be indicative of the effect of El Niño-like conditions, even in the absence of a formal designation, and give some idea that the regional patterns have shifted in favor of El Niño formation.

El Niño Tracker Update - December 2014

Friday, December 19, 2014

From the Dec 18, 2014 - Southwest Climate Outlook - 

We are still waiting for a decisive signal, but conditions indicate we are near, or possibly already into, at least a weak El Niño event. Sea surface temperatures (SSTs) are elevated across the equatorial Pacific Ocean (Fig. 1), and the measurements in the Niño 3.4 region are indicative of El Niño having already started (Fig. 2).

There remains a distinct lack of cooperation on the part of the atmosphere. This lack of coupling between ocean and atmosphere (demonstrated by near-normal wind and rainfall anomalies), along with a lack of temperature gradient along the equatorial Pacific and little in the way of El Niño wind patterns, means that while we are likely already experiencing El Niño-like conditions in the Southwest (e.g. some of the recent wet weather), it may be a little longer before a formal declaration occurs, even if retroactively.  

On Dec. 4, the NOAA-Climate Prediction Center (CPC) issued another El Niño Watch, with a 65 percent probability of a weak El Niño event occurring.  Anomalous SSTs alone were probably enough to suggest a weak El Niño event, but the lack of atmospheric coupling kept the current assessment at ENSO-neutral.  On Dec. 10, the Japan Meteorological Agency declared that an El Niño started in late summer and that it would continue through early 2015. This was based on favorable El Niño conditions and elevated SSTs, even while other more robust criteria were not yet met. On Dec. 16, the Australian Government’s Bureau of Meteorology maintained its El Niño tracker status at El Niño Alert status, despite a lack of atmospheric conditions to complement the anomalous SSTs. That outlook assigned a 70 percent probability of a weak El Niño event developing in winter 2014–2015. The Dec. 18 International Research Institute for Climate and Society (IRI) and CPC upped the probability of El Niño conditions developing to more than 80 percent in the next three months and more than 70 percent through spring and into summer (Fig. 3).

The North American multi-model ensemble shows a weak event that extends well into spring (Fig. 4). The extended period of above-average SSTs appears to be increasing confidence in the formation of El Niño this winter into spring.

Seasonal precipitation forecasts still indicate an enhanced chance of above-average precipitation over the upcoming winter, but confidence in this forecast is partially contingent on the strength of the emerging El Niño event. The impacts associated with weak El Niño events are generally less certain than those of a moderate or strong event, with past weak events bringing both dry and wet conditions to the Southwest U.S. during the winter. Ultimately, the above-average tropical storm season and the humidity that has remained in the region may be indicative of the effect of El Niño-like conditions, and we may be seeing the emergent effects of El Niño impacts on the climate of the Southwest, despite the absence of a formal definition identifying the start of a bounded El Niño event.

What is El Niño? - From the SW Climate Podcast

Monday, December 1, 2014

This mini-segment was taken from the November 2014 Southwest Climate Podcast


Image & Story Credits

El Niño Tracker Update - Late November 2014

Friday, November 21, 2014

From the Nov 20, 2014 Southwest Climate Outlook

The long-awaited El Niño event projected to develop during winter 2014 – 2015 has yet to send a decisive signal regarding an official start, but a number of factors have increased forecasters’ confidence that one will emerge. The strength of this event still remains in question, however with the most likely projection still centering on a weak or weak to moderate event.

On Nov 6, the NOAA-Climate Prediction Center (CPC) issued an El Niño Watch, assigning a 58 percent probability that an El Niño would form and that it most likely would be weak. This forecast was based on a slight increase of sea surface temperatures (SSTs) across the eastern equatorial Pacific, linked to the contribution of the Kelvin wave (discussed last month), which helped warm SSTs in the eastern Pacific.  The CPC also reported the “ongoing lack of clear atmosphere-ocean coupling” (discussed in our previous Southwest Climate Podcasts) reduced confidence in the forecast.  On Nov 18, the Australian Government Board of Meteorology increased its El Niño tracker status from El Niño Watch to El Niño Alert, with a 70 percent probability of an El Niño developing in winter 2014–2015.  This outlook was based on a recent surge in above-average temperatures in the tropical Pacific Ocean (Fig. 1) and the Southern Oscillation Index (Fig. 2), which exceeded the El Niño threshold for the past three months, despite a lack of complete cooperation on the part of atmospheric conditions.

The Nov. 20 International Research Institute for Climate and Society (IRI) and CPC forecast reiterated these points, as the SSTs have exceeded the threshold for weak El Niño conditions, even while some of the atmospheric variables have yet to point towards an El Niño event. The mid-November forecast subsequently upped the probability of El Niño conditions developing to 75 percent (Fig. 3), and the North American multi-model ensemble shows a weak to moderate event peaking in mid to late winter and extending into the spring (Fig. 4).  

The strength of the event, if and when it forms, will matter. The impacts associated with weak El Niño events are generally less certain than those of a moderate or strong event, with past weak events bringing both dry and wet conditions to the Southwest U.S. during the winter. Seasonal precipitation forecasts still indicate an enhanced chance of above-average precipitation over the upcoming winter, but confidence in this forecast is partially contingent on the strength of the emerging El Niño event. It should also be noted that the signal for the Pacific Decadal Oscillation (PDO) has moved into a positive phase, which bodes well for increased precipitation this winter, especially since the El Niño-Southern Oscillation (ENSO) and PDO signals have the potential to enhance, rather than work against, the other.

SW Climate Podcast - Mini-Video Podcast on El Niño and ENSO Models

Tuesday, October 21, 2014

 

Next up in our new series featuring video mini-segments from the podcast.  This segment comes from the September 2014 SW Climate Podcast - and covers ENSO models and El Niño forecasts.

Mike Crimmins and Zack Guido talk about El Niño forecast models and the way that different metrics are used to predict/forecast an El Niño event.

Taken from the CLIMAS Southwest Climate Podcast

  • Mike Crimmins - CLIMAS: Climate Assessment for the Southwest & University of Arizona Cooperative Extension
  • Zack Guido - University of AZ International Research and Application Program (IRAP)
  • Ben McMahan - CLIMAS: Climate Assessment for the Southwest
  • Emily Huddleston - CLIMAS: Climate Assessment for the Southwest

Image Credits (in order of appearance):

  • Sea Surface Temperature Anomalies - April to December during building El Niño - ​Source: NOAA/Climate.gov
  • Global Sea Surface Anomalies - La Niña (1988) vs El Niño (1997) - Source: NOAA/Climate.gov
  • Ocean SST anomalies during ENSO cycle - Source: http://bobtisdale.wordpress.com
  • Mid-Sept IRI/CPC Plume-Based Probabilistic ENSO Forecast - Source: IRI/CPC
  • April/May/June SST in Pacific Ocean - Source: NOAA/Climate.gov
  • Mid-Sept 2014 Plume of Model ENSO Predictions - Source: IRI/CPC
  • Oceanic Niño Index (ONI) over time - Source: NOAA/CPC
  • El Niño vs. La Niña Winter Patterns  - Source: NOAA

If you have a question you'd like answered, you can email Zack Guido (zguido@email.arizona.edu) or Ben McMahan (bmcmahan@email.arizona.edu) with "CLIMAS Podcast Question" in the subject line.  You can also tweet us @CLIMAS_UA or post a question on facebook

2014/2015 El Niño Tracker: Oct 16, 2014

Thursday, October 16, 2014

An El Niño Watch, issued by the NOAA Climate Prediction Center (CPC), continues for the seventh consecutive month as signs of an emerging El Niño are just on the horizon, but not quite here yet. Another slug of warm water (also known as a Kelvin wave), has been making its way across the Pacific Ocean from west to east just below the surface and is poised to emerge and help warm sea surface temperatures in the eastern Pacific over the next month or so. Westerly wind bursts, which help move this warmer-than-average water to the east, have occurred in the western and central Pacific but have been temporary and haven’t helped sustain a steady progression towards El Niño conditions, which typically peak during mid-winter. 

Forecast models are betting the current Kelvin wave and associated warm water in the east Pacific will finally get this fickle event to organize and roll forward as a weak El Niño; only a handful of models suggest a moderate-strength event. The early-October consensus forecast (Fig. 1) issued by the International Research Institute for Climate and Society (IRI) and the CPC still indicates more than a 65 percent chance of El Niño conditions developing during the November-December-January period and most likely persisting through early next spring. The impacts associated with weak El Niño events are much less certain than with stronger events, with similar past events bringing both dry and wet conditions to the Southwest U.S. during the winter. Seasonal precipitation forecasts still indicate an enhanced chance of above-average precipitation over the upcoming winter, but confidence in this forecast has wavered slightly because of the expected weak nature of the emerging El Niño. 

This post was originally published as part of the October 2014 Southwest Climate Outlook

El Niño Tracker - Sept 2014

Thursday, September 18, 2014

The song remains the same this month with El Niño not quite here yet, but probably soon. This is now the seventh consecutive month since the NOAA Climate Prediction Center issued an “El Niño Watch” last March. The signs are a bit stronger once again, but it is getting late in the game since El Niño events take several months to build up and typically peak during the mid-winter months. Another slug of warm water (known as a “Kelvin Wave”) has been making its way across the Pacific Ocean from west to east just below the surface and is poised to emerge and help warm sea-surface temperatures in the eastern Pacific over the next month or so. There has also been some activity in the western and central Pacific called “westerly wind bursts” which can help move this warmer-than-average water to the east, but the bursts have been temporary and haven’t helped sustain a steady progression towards El Niño conditions. 

Forecasts models are predicting the current Kelvin Wave and associated warm water in the east Pacific will finally get this fickle event to organize and roll forward as at least a weak El Niño. The mid-September consensus forecast (Figure 1) issued by the International Research Institute for Climate and Society (IRI) and the NOAA Climate Prediction Center (NOAA-CPC) still indicate a greater than 70 percent chance of El Niño conditions developing during the November-December-January period and most likely persisting through early next spring. Most models indicate that the event will ultimately peak at a weak strength, with only a handful of models suggesting a moderate-strength event. The impacts associated with weak El Niño events are much less certain; past events have brought both dry and wet conditions to the southwest U.S. during the winter season. Seasonal precipitation forecasts still indicate an enhanced chance of above-average precipitation over the upcoming winter season, but confidence in this forecast has wavered slightly because of the expected weak nature of the emerging El Niño event.

This post was originally published as part of the September 2014 Southwest Climate Outlook

El Niño Watch - Aug 21, 2014

Thursday, August 21, 2014

An “El Niño Watch” continues this month as issued by the NOAA Climate Prediction Center several months ago. The watch is just that: we are waiting and watching for the development of a full-fledged El Niño event that has yet to materialize across the equatorial Pacific Ocean. Several indicators of El Nino-Southern Oscillation (ENSO) status declined, moving back towards ENSO-neutral values over the past month instead of leaning towards an El Niño event as they had been.  These shifts included slight cooling in the eastern Pacific Ocean and near-average wind patterns along the equator (Figure 1). But for those cheering on the development of an El Niño event, not all hope is lost. A slug of warm water just below the surface has materialized in the western Pacific Ocean and is slowly moving eastward.  This is similar to the pulse of warm water that led to dramatic warming in the eastern Pacific Ocean earlier this spring. This “Kelvin Wave” is not as strong in magnitude as the earlier springtime wave, but is expected to surface in the eastern Pacific over the next several months, pouring fuel back into the El Niño engine.

Seasonal ENSO outlooks pick up on this pattern and remain rather bullish in suggesting that an El Niño event is likely later this fall that would peak in early winter (Figure 2). The models suggest this would be a moderate event at best; in fact most models suggest a weak El Niño event of around 1 degree C above average in sea-surface temperatures in the central/eastern Pacific Ocean. The weaker the event, the trickier the forecast with respect to expected precipitation across Arizona and New Mexico. Weak El Niño events vary between wet, near average, and even dry winters in historical records across the Southwest. Official seasonal precipitation forecasts continue to suggest an enhanced chance of above-average precipitation across Arizona and New Mexico through the winter, but confidence in these forecasts is tied to the development and ultimate strength of the El Niño event that has yet to materialize.

This post was originally published as part of the August 2014 Southwest Climate Outlook

Notes from an Applied Climatologist: Q & A on El Niño, Predictions, and Indices

Wednesday, August 13, 2014

 

What is the criteria to call something El Niño?  Is El Niño a continuum or is there a binary switch where it's either an El Niño event or not?

There are actually several different indices or metrics used to track the state of ENSO (the El Niño-Southern Oscillation) across the Pacific Ocean and whether oceanic and atmospheric patterns reflect El Niño, La Niña or neutral conditions. Some of these indices look just at the atmosphere (for example Southern Oscillation Index), some just at the ocean (for example Niño3.4 index) and some the combination of both (for example the Multivariate ENSO Index). All have different strengths and weaknesses, but oceanic based indices tend to reflect the more slowly evolving part of ENSO, the shift in sea surface temperature patterns, which in turn can have an impact on global weather patterns over many months or seasons.

The NOAA Climate Prediction Center uses the Oceanic Nino Index (ONI) which is the running 3-month average of sea surface temperature anomalies (or departures from average) across a key part of the central equatorial Pacific from just west of the International Date Line back towards the east to 120W longitude.

Tracking sea temperatures in this region provides a good indication of whether or not tropical convection (which is driven by warm waters) is shifting or may soon shift unusually far east along the equator during El Nino conditions or far west during La Nina events. ONI values typically range from -2.5 which would be indicative of a strong La Nina to 2.5 which would be a strong El Nino event. The NOAA-CPC makes a distinction between the emergence of El Nino or La Nina conditions which would be ONI values climbing past the +0.5 (El Nino) or -0.5 threshold at the monthly scale as well as other atmospheric indications like shifts in wind and rainfall patterns versus a full blown event that lasts for many months or over seasons. An event requires ONI values to be greater than the +0.5 or -0.5 threshold for at least five consecutive months (more details at climate.gov)

 

How closely linked is the strength of El Niño with observable effects in the Southwest?  Would a weak El Niño look that different from no El Niño at all?  

The strength of an El Nino event does seem to matter with respect to seasonal climate connections here in the Southwest. Looking at past precipitation patterns during El Nino winters of varying strengths, you notice that strong events (ones with ONI values >1.5) tend to have a more reliably wet look to them versus weak events which vary from above-average to even below-average.

The forecast of a strong El Nino event tends to lead to a subsequently more confident outlook in wet conditions for Arizona and New Mexico. If the event is forecasted to be weak or even moderate the outlook for precipitation over the upcoming winter season is much less certain (more on this topic climate.gov)

Michael Crimmins is an Associate Professor and Climate Science Extension Specialist in the Department of Soil, Water and Environmental Science

Notes from an Applied Climatologist: El Niño & Drought Q&A

Wednesday, August 6, 2014

 

There’s been a lot of talk about El Niño and ‘busting the drought'.  How much can El Niño help with ongoing drought conditions in the West?

The El Niño event struggling to form in the Pacific Ocean has been a ray of hope for many of us across the Southwest for several months now looking for some relief from both short and long-term drought conditions that have plagued California, Arizona and New Mexico for several years now. The important thing to remember is that we can only expect *some* relief in a best case scenario with a strong El Niño event delivering abundant precipitation across the Southwest over the winter season. Current drought conditions have accumulated over years and cannot be erased by a single wet season. We can look back at drought indices around the time of the last strong El Niño event over the winter of 1997-1998.

For a detailed look at Standardized Precipitation Index (SPI) in Arizona - Click Here

Wet conditions were observed across Arizona over several months which dramatically improved short-term drought conditions (months to seasons), but longer term drought conditions (seasons to years) were still present and quickly intensified as dry conditions returned the following year. At this point we will need several years of average to above-average precipitation over each season to alleviate long-term drought conditions. An El Niño winter with above-average precipitation would help, but is not a silver bullet at this point.

 

Significant amounts of rain fall during the monsoon, why doesn’t that solve our drought problems?

Monsoon precipitation is a critical water source to many ecosystems and agricultural activities (e.g. ranching), and is an important determinant of drought status during the summer across the Southwest. If monsoon precipitation is spotty, late in onset, and overall below-average, short-term drought conditions can quickly intensify across Arizona and New Mexico. As far as long-term drought conditions that evolve over multiple seasons or years, a single monsoon season typically has little impact.

Dry conditions during the summer can contribute to long-term drought impacts like stress in trees and reductions in surface water streamflows, but average to wet conditions often don’t contribute much to improvements. Monsoon precipitation typically falls in torrents of heavy rain associated with isolated storms, leaving a patchwork of runoff and wet soil that quickly evaporates back into the atmosphere. Occasionally, large-scale flooding events during the summer can lead to high flows in streams and contributions to reservoirs and subsequent relief from long-term drought impacts, but these events are rare and unpredictable.  


Michael Crimmins is an Associate Professor and Climate Science Extension Specialist in the Department of Soil, Water and Environmental Science

Notes from an Applied Climatologist: Monsoon & El Niño Q&A

Thursday, July 31, 2014

 

Is the strong start to the monsoon related to El Niño?

In short? Probably not. Research on the interactions between El Niño events and the North American Monsoon System actually suggests the opposite, with past El Niño events slowing the onset of monsoon precipitation across the Southwest U.S.  

This year, when compared to records of average dewpoints across Arizona and New Mexico, the monsoon moved in right on time.  It was ushered in by surges of moisture that moved up the Gulf of California into the desert Southwest, several of which were triggered by tropical storms and hurricanes in the eastern Pacific that flourished in highly favorable conditions, including light upper level winds and very warm ocean water.  These conditions are not necessarily related to El Niño, as conditions that favor an El Niño event have largely been absent in the atmosphere, with only glimmers of a favorable pattern in the sea surface temperatures across the eastern Pacific Ocean. The fact that the current El Niño has been struggling to form may also be the reason we had a relatively "normal" start to the monsoon.

More precipitation maps at http://cals.arizona.edu/climate/misc/monsoon/az_monsoon.html

 

What can we expect from the monsoon (in AZ & NM) with El Niño waiting in the wings?

Research on the interactions between El Niño and the North American Monsoon System suggest that the impact of El Niño is largely observed early in the season, primarily in the months of June and July. This means that even with an El Niño (probably) forming later this summer, its direct impact on the monsoon will likely be minimal.

An indirect effect continues to be the very favorable tropical storm and hurricane conditions in the eastern Pacific related in part to the struggling El Niño event. With more tropical storm activity in the eastern Pacific there is an elevated chance that one of these storms will curve back to the east and visit the Southwest, especially later in August and September. Some of the floods of record across Arizona and New Mexico are related to late monsoon season tropical storms curving back through the Southwest.


Michael Crimmins is an Associate Professor and Climate Science Extension Specialist in the Department of Soil, Water and Environmental Science

El Niño Watch - July 18, 2014

Friday, July 18, 2014

Originally published in the Southwest Climate Outlook, released the 3rd Thursday of every month.  Sign up for email newsletter version.


The El Niño event that has been anticipated for the past several months continues to suffer from stage fright; it has yet to fully materialize across the equatorial Pacific Ocean. Nonetheless, forecasts remain bullish that an El Niño will form in coming months, and consequently the El Niño Watch is still in place. Probabilities that an El Niño will fully materialize this fall and winter reach slightly more than 70 percent, according to the mid-July ENSO forecast issued by the NOAA-Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI; Figure 1). These high probabilities reflect above-average sea surface temperatures (SSTS) in the far eastern Pacific and weak westerly winds in the central Pacific. Belief that this event will evolve into a strong El Niño, however, has lost muster because SSTs have hovered slightly above average and not steadily climbed (Figure 2). In addition, the atmosphere has failed to cooperate in a manner consistent with above-average SSTs. For an El Niño to gain strength, the warming SSTs in the central Pacific need to be accompanied by a subsequent weakening of the easterly trade winds which, in turn, reinforce warm SSTs. The easterly winds have yet to slacken as much as expected.

Nonetheless, the CPC forecast suggests that both the ocean and atmosphere are transitioning to and ultimately will become an El Niño. Feeding this expectation is the observation that convection in the central Pacific has become more organized in recent weeks. This indicates a growing atmospheric connection with the SSTs that could eventually lead to a weakening of the trade winds. Moreover, many of the dynamical forecast models (those that included both ocean and atmosphere dynamics) suggest a rapid warming in the central Pacific during the August–October period, with the El Niño event peaking in mid-winter of 2014 and 2015. Although the ultimate strength and duration remains uncertain, a weak to moderate event appears the most likely outcome, and the CPC notes the possibility for a strong event has diminished greatly in the past several months.

El Niño events tend to bring wetter conditions to the Southwest during the winter (Figure 3), with moderate and strong events delivering higher chances for above-average precipitation. However, if the El Niño event is weak, the precipitation outlook for the upcoming fall and winter becomes more uncertain. The strength and duration of the event should become clearer over the next two months as ocean and atmosphere signals lock in to each other.