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Southwest Climate Outlook May 2016 - Climate Summary | CLIMAS


Southwest Climate Outlook May 2016 - Climate Summary

Thursday, May 19, 2016

Originally published in the May 2016 CLIMAS Southwest Climate Outlook

Precipitation & Temperature: Across most of the Southwest, April 2016 precipitation totals were above average (Fig 1a) and temperatures were average to above average (Fig 1b). Over the past 30 days, the Southwest experienced a minor cooling trend, with much of the region recording below-average temperatures (Fig. 2a) and a mix of above- and below-average precipitation (Fig. 2b). Increased rainfall and below-average temperatures are a welcome, albeit temporary, break from the typical warming and drying trend observed in late spring and early summer.

Drought, Snowpack and Water Supply: Long-term drought persists across the Southwest (Fig. 3). El Niño’s middling performance did little to alter the trajectory of long-term drought, despite hope and optimism for just such a possibility leading into the winter season. The increasingly likely return of La Niña conditions this fall raises the specter of drier-than-average conditions for the Southwest, which could further exacerbate long-term drought. Reservoir storage values reflect this persistent drought with Lakes Mead and Powell in Arizona and Elephant Butte Reservoir in New Mexico at 37, 45, and 15 percent of capacity, respectively (see reservoir storage diagrams on page 6 for more details). Snowpack is mostly gone in the lower Southwest, while the upper basin regions of Colorado and Utah and northern New Mexico still have snow water equivalent (SWE) values ranging from 50 to 150 percent of normal (Fig. 4). Water year precipitation to date (October 1 to present) is normal to below normal across most of Arizona and normal to above normal for most of New Mexico. 

El Niño Tracker: El Niño is in decline and forecasts call for continued weakening, leading to an ENSO-neutral state by summer and an increasing possibility of La Niña conditions by fall. The climatology of the Southwest in late spring and early summer is typically warm and dry, but there have been a few late season pulses of moisture that have helped bring below-average temperatures and some upper elevation precipitation to the region. This activity is not expected to bring significant additional precipitation, as sufficient moisture to help fuel these storms is unlikely. This intermittent activity may not alter seasonal cumulative precipitation totals significanlty, but these events are helpful in suppressing wildfire risk and delaying the onset of the intense heat of pre-monsoonal summer.

Environmental Health and Safety: Warm and dry conditions over the winter have exacerbated already dusty conditions associated with both land-use change and long-term drought, with notable hazards in particularly dangerous stretches of Interstate-10 in both Arizona and New Mexico. Wildfire season is well underway, and while intermittent moisture in April helped tamp down fire risk, fine fuel growth from a wet fall combined with dry conditions this winter have contributed to above-normal wildland fire risk for the rest of May and June (Fig. 5).

Precipitation and Temperature Forecast: The May 19 NOAA-Climate Prediction Center three-month seasonal outlook calls for equal chances of above- or below-average precipitation for the Southwest (Fig. 6, top) and increased chances of above-average temperatures across most of the western United States (Fig. 6, bottom).