Southwest Climate Outlook May 2021

Date issued

Precipitation and Temperature: April precipitation was between record driest and average in most of Arizona and between much below average and above average in most of New Mexico (Fig. 1a). April temperatures were above average to much above average in Arizona and average to much above average in most of New Mexico (Fig. 1b, SW Temps), with similar patterns for 2021 so far (Fig. 2).

Drought: Water year precipitation to date is between below normal and much below normal across most of the Southwest, with record driest conditions in parts of CA/NV/AZ (Fig. 3). The U.S. Drought Monitor (USDM) is mostly unchanged from last month in the U.S. Southwest (Fig. 4), although California did see some expanded drought designations. This is partly because much of the region is at the highest drought category (D4, Exceptional Drought) and the scale simply does not go any drier. In Arizona and New Mexico, over 50-percent of the region is in D4, and 80-85 percent is in at least D3 (Extreme Drought).

Snowpack and Water Supply: Snow water equivalent (SWE) is well below the 1981-2010 median for the higher elevation regions that feed into streams over summer (see the NRCS website for details). Streamflow forecasts are below median across the Southwest, and are below fifty percent of the median in many of the upper sub-basins for the Colorado and Rio Grande rivers (Fig. 5). Most of the reservoirs in the region are at or below the values recorded at this time last year. Most are below their long-term average (see Arizona and New Mexico reservoir storage).

Wildfire: Wildfire season is already underway in Arizona. The National Interagency Fire Center (NIFC) maps of significant fire potential call for above-normal wildfire risk across all of Arizona and New Mexico in May and June (Fig. 6). Wildfire risk in the Southwest will see increased ignition sources with the onset of the monsoon and the potential for dry lightning, especially before monsoon precipitation begins in earnest.

ENSO Tracker: La Niña conditions have ended for now, and the outlooks and forecasts have reverted to ENSO-neutral. The long-term forecasts see a possible return to La Niña conditions this winter, but it will be a wait-and-see situation over much of summer given the uncertainty (see ENSO-tracker for details).

Precipitation and Temperature Forecast: The three-month outlook for June through August calls for increased chances for below-normal precipitation across much of the southwestern U.S., particularly in a swath extending from New Mexico into northern Mexico (Fig. 7, top). The three-month temperature outlook calls for increased chances of above-normal temperatures across much of the southwestern U.S. and portions of northern Mexico (Fig. 7, bottom).

Published by the Climate Assessment for the Southwest (CLIMAS), with support from University of Arizona Cooperative Extension, the Arizona State Climate Office, and the New Mexico State Climate office.

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