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Monthly Archive

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

Monsoon Summary Jun 15-Aug 20

Friday, August 21, 2015

Originally published in the August 2015 CLIMAS Southwest Climate Outlook

The monsoon started off early and strong with several widespread thunderstorms in late June and early July, especially in Arizona, which recorded its second wettest June on record.  Precipitation tapered to some extent in July in Arizona but continued to be frequent and widespread in New Mexico, which recorded its 10th wettest July on record (Figs. 1a-2a).  

Overall monsoon activity has taken a break thus far in August, although a few powerful and localized storms brought significant precipitation to portions of Arizona. This pattern is a defining characteristic of the 2015 monsoon, particularly in Arizona, where many of the monsoon storms have been highly localized, dropping heavy precipitation in smaller areas and often on high elevation peaks instead of more widespread and systematic monsoon activity. Portions of southern Arizona and the Four Corners region—areas that saw considerable precipitation deficits in the past few years—have been the beneficiaries of this variable coverage, especially in the past few weeks. This pattern may change if the monsoon ridge sets up further east, allowing for more organized storm activity to flow in from the south in the coming weeks, or if later-season eastern Pacific tropical storm activity ramps up and helps drive moisture into the region. 

We also have seen some weakening of the monsoon ridge since July 5, likely due to El Niño convection picking back up, but it remains to be seen what the overall impact of El Niño will be on this year’s monsoon. Regional dewpoint readings also illustrate the variability of monsoon activity, particularly in July and into August (Fig. 2).

In the first two months of the monsoon, most of northern Arizona and nearly all of New Mexico recorded above-average precipitation (Figs. 3a–b), albeit with a wide range of precipitation totals across the region (Figs. 4a–b). Southwestern Arizona, particularly the southwest and northwest corners, are notable exceptions to this pattern, although these areas typically receive far less monsoon precipitation overall. The percent of days with rain highlights the regularity of monsoon precipitation thus far, with much of eastern Arizona and nearly all of New Mexico recording rain events (greater than 0.01 inch) on 35 to 50 percent of days since June 15 (Figs. 5a–b). The daily intensity index (Figs. 6a–b) further illustrates the steady nature of most of this monsoon precipitation; higher values indicate much of the rain fell in a single event and lower values indicate more frequent and less intense events.

August 2015 - CLIMAS Southwest Climate Outlook

Thursday, August 20, 2015

Precipitation: In the past 30 days, much of southern Arizona and New Mexico received below-average precipitation, with portions of northern Arizona and New Mexico recording above-average precipitation (Fig. 1). In August, below-average precipitation has been punctuated by a few intense storm systems, mostly in Arizona. For New Mexico, July was the 10th wettest month on record. In general, the precipitation events that have occurred have been more localized storm systems, resulting in highly variable precipitation across the region (see Monsoon Tracker, pages 5-6).

Image Source - High Plains Regional Climate Center

Temperature: After a record warm start to 2015, much of the Southwest cooled off in July, especially in Arizona (Fig. 2). This respite was short-lived however, as temperature anomalies in the past 30 days were between 0 and 6 degrees F above normal across most of New Mexico and most of Arizona (Fig. 3). Globally, 2015 likely will challenge 2014 for warmest year on record, a trend that could affect temperature trends in the Southwest.

Image Source - High Plains Regional Climate Center

Monsoon: The highly variable nature of the monsoon in terms of when and where rain falls poses a serious challenge to anyone attempting to characterize the monsoon. That said, summer 2015 has been relatively typical, with average to above-average rainfall across much of Arizona and more consistent and sustained above-average precipitation in New Mexico. We also have seen expected breaks in storm activity as the monsoon ridge moves, affecting regional patterns of precipitation—or lack thereof—across the region (see Monsoon Tracker, pages 5–6 for a more detailed discussion).

Drought & Water Supply: The U.S. Drought Monitor continues to emphasize drought conditions across the West, with particularly severe conditions in California and Nevada (Fig. 4). Arizona and New Mexico continue to grapple with years of accumulated drought and water deficits, but recent sustained and widespread precipitation has helped slightly scale back drought conditions, particularly in New Mexico (see Reservoir Volumes, page 7).

Wildfire: As of July 31, wildland fires had burned approximately 120,000 acres in Arizona and about 40,000 acres in New Mexico. One notable blaze was the Finger Rock fire, which ignited in the Santa Catalina Mountains in southern Arizona and was visible from Tucson for a number of days. Favorable weather conditions allowed fire managers to let the fire burn out naturally, despite proximity to residential areas. This fire season, well above-average precipitation in Arizona in June and in New Mexico in July tamped down fire risk across the region, resulting in limited regional fire and fire suppression activity, and favorable weather conditions permitted a number of fires to be left to burn, benefitting forest health. 

Precipitation & Temperature Forecasts: The Aug. 20 NOAA-Climate Prediction Center seasonal outlook predicts above-average precipitation for most of the Southwest and Intermountain West this summer (Fig. 5, top). Notable exceptions are northern California and far northwestern Nevada. Temperature forecasts are split, with elevated chances for above-average temperatures along the West Coast and into western Arizona (and most of the western U.S.), and increased chances for below-average temperatures centered over Oklahoma and Texas and extending across New Mexico (Fig. 5, bottom). It remains to be seen what effect eastern Pacific tropical storms and El Niño will have on these patterns.

Image Source - NOAA/NWS - Climate Prediction Center

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