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Monthly Archive

SW Climate Outlook - Monsoon Case Study - Tucson July 2017

Tuesday, July 25, 2017

The onset of monsoon activity seemed to arrive late in Tucson this year, although residents have been rewarded for their patience by a surge of almost daily storms in the region since July 10. Coincidentally, July 10 was also the third straight day of average daily dewpoint temperatures at or above 54 degrees, thereby meeting the monsoon threshold used by NWS Tucson prior to 2008. The average start date by the former definition is around July 3, although in 2015 and 2016 Tucson met this threshold on June 25. By the dewpoint criteria—and given the absence of any measurable precipitation in Tucson in June and early July, the monsoon did start late, but as was discussed in the most recent episode of the CLIMAS Southwest Climate Podcast, the relatively short length of the monsoon and the desire for relief from the extreme heat of June means any delay to the onset feels like an eternity, even if the first big storm day is only a few days or a week after we might normally expect it.

The recent surge of precipitation in southern Arizona has dramatically boosted seasonal totals: the recording station at the Tucson International Airport jumped from zero percent of normal on July 9 to nearly 200 percent of normal by July 19 (Fig. 3). This example illustrates two important points about monsoon-related data:

1) The temporal variability of the monsoon means that daily or weekly tracking can be deceptive, and over the 108 days of the official season, there will be bursts and breaks of activity, with greater chances occurring during the height of the season from early- to mid-July through mid- to late August;

2) Single stations do not capture the spatial variability of the monsoon – a quick visit to rainlog.org on any given storm day will demonstrate the high degree of variability across relatively short distances.

SW Climate Outlook - Monsoon Tracker - July 2017

Monday, July 24, 2017

The official start date of the monsoon (June 15) was overshadowed by a Southwest-wide extreme heatwave that set numerous records. Heatwaves in June are a typical feature of the seasonal climate, especially as the subtropical ridge builds north, but these record temperatures also increased the anticipation for the relief that the monsoon can provide. Much of southern and central Arizona have recorded pockets of above-average precipitation, while New Mexico has seen more widely distributed precipitation since June 15 (Fig. 1a-b). The maps highlight the extreme spatial variability of monsoon precipitation and the difficulty of scoring or grading the monsoon performance using single stations or summary maps (not that we don’t continue to try!). Another useful metric is the percent of days with rain, which, when used with the precipitation maps, distinguishes areas that have received more frequent and moderate precipitation from those in which just a few extreme events boosted seasonal totals. In Arizona, the southeastern corner and a swath across the higher-elevation areas of the central part of the state have received the most consistent precipitation, with significant variability across other areas (Fig. 2a). In contrast, precipitation frequency is relatively uniform across most of New Mexico, reflecting an earlier start to the monsoon as well as more overall precipitation activity (Fig. 2b).

SW Climate Outlook - ENSO Tracker - July 2017

Friday, July 21, 2017

Oceanic and atmospheric indicators are still within the range of neutral (Figs. 1-2), although sea-surface temperatures have hinted at borderline El Niño conditions. Seasonal outlooks and forecasts generally agree that ENSO-neutral conditions are the most likely outcome for the remainder of 2017, albeit with a lingering possibility of an El Niño event by winter 2017-2018.

On July 10, the Japanese Meteorological Agency (JMA) identified a continuation of ENSO-neutral conditions with an 80-percent chance of them extending through fall 2017. On July 13, the NOAA Climate Prediction Center (CPC) observed that oceanic and atmospheric conditions were consistent with ENSO-neutral conditions, maintaining a 50-55-percent chance of ENSO-neutral conditions in 2017 and a 35-45-percent chance of an El Niño. On July 18, the Australian Bureau of Meteorology effectively ended their El Niño watch, citing little evidence for anything other than neutral conditions at this point. On July 20, the International Research Institute for Climate and Society (IRI) and CPC identified a 35-40-percent chance of an El Niño in 2017 (Fig. 3) with “ENSO-neutral as the most likely condition during 2017.” The North American Multi-Model Ensemble (NMME) is ENSO-neutral as of July 2017. The model spread indicates a range of outcomes for the rest of 2017 (Fig. 4), but the ensemble mean indicates ENSO-neutral as the most likely outcome, yet allowing that a weak El Niño event is plausible.

Summary: The lack of atmospheric indicators of El Niño and the borderline status of sea-surface temperature anomalies have further contributed to forecaster consensus that ENSO-neutral conditions are the most likely outcome for 2017. An El Niño event remains possible but looks increasingly unlikely. As with last month, two key conclusions can be drawn from the current outlooks and forecasts. One, the probability of a La Niña event in 2017 is near zero, which is good news considering La Niña winters are often warmer and drier than normal in the Southwest. Two, given the relatively weak correlation between cool-season precipitation and weak El Niño events, it doesn’t really matter whether this winter ultimately turns out as ENSO-neutral or weak El Niño, as the winter seasonal precipitation outlook for the Southwest will encompass a wide range of possible outcomes, including both wetter and drier than normal conditions.

SW Climate Outlook July 2017 - Climate Summary

Thursday, July 20, 2017

Precipitation and Temperature: June precipitation ranged from record driest to near average in Arizona, while in New Mexico, precipitation ranged from much-below to much-above average (Fig. 1a). This difference reflects the seasonal progression of monsoon activity in the Southwest—it typically starts earlier in New Mexico and progresses westward—as well as the relatively late start to monsoon activity observed in much of Arizona this year. June temperatures ranged from much-above average to record warmest in Arizona and from above average to much-above average in New Mexico (Fig. 1b). A region-wide heat wave that struck in mid-to-late June helped drag up the averages, setting a number of daily high records across Arizona. Year-to-date precipitation ranks reveal average to above-average precipitation in all of New Mexico and much of Arizona, with a pocket of below-average precipitation in southeast Arizona (Fig. 2a). Year-to-date temperatures reveal much-above-average to record-warmest conditions in both Arizona and New Mexico (Fig. 2b).

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Monsoon Tracker: The official start of the monsoon was June 15, but widespread activity started relatively late this year (see monsoon discussion), especially in southern Arizona. There, numerous storms in mid-July brought widespread and frequent precipitation activity, boosting the percent normal monsoon precipitation in several locations (See Figs. 1a-b on SW Monsoon Tracker). New Mexico had a comparatively earlier start to monsoon activity, which is expected given the typical spatiotemporal progression of the monsoon (Fig. 3), and has seen more steady and widespread monsoon activity, as evidenced by the percent of days with rain (see Figs. 2a-b on SW Monsoon Tracker).

Drought & Water Supply: Drought conditions on the U.S. drought monitor have expanded in the past few weeks, with most of Arizona recording either D0 (abnormally dry) or D1 (moderate drought) conditions. This reflects short-term precipitation deficits in the upper two-thirds of Arizona, as well as short- and long-term deficits in the lower third, a pattern that also extends to the southwestern corner of New Mexico. Most of the rest of New Mexico has no drought designation (Fig. 4).

Wildfire: Arizona is experiencing an active fire season in 2017, with nearly 350,000 acres of wildfire across the state. A number of factors contributed to the increased activity in Arizona this year, including abundant fine fuels, below-average winter precipitation, above-average temperatures, and a later-than-average start to the monsoon and its increased precipitation and relative humidity. New Mexico has had less fire activity, with approximately 123,000 acres burned, largely attributed to the earlier arrival of monsoon conditions.

El Niño Southern Oscillation: Most models and forecasts continue to suggest the most likely outcome for 2017 is ENSO neutral conditions through winter 2017-2018 (50-55 percent chance). The chances of an El Niño event do remain elevated (35-45 percent chance) compared to long-term averages, however, effectively reducing the chance of a La Niña event to near zero.

Precipitation and Temperature Forecast: The July 20 NOAA Climate Prediction Center’s outlook for August calls for increased chance of above-average precipitation in Arizona and New Mexico, and equal chances of above- or below -average temperatures in most of Arizona and New Mexico. The three-month outlook for August through October calls for increased chance of above-average precipitation in Arizona and New Mexico (Fig. 5, top). Increased chances of above-normal temperatures are forecast for the entire United States (Fig. 5, bottom).