The University of Arizona

Climate Snapshot | CLIMAS

 SW Climate Outlook

Climate Snapshot

Climate Snapshot (data between June 20-November 21, 2013 )
Data Source(s): Western Regional Climate Center

Temperatures in November have been September-like across the Southwest; the mild conditions have been the climate story of the last month. This is most pertinent in southeastern Arizona where minimum, maximum, and average temperatures have ranged between 2 and 5 degrees F above average.

October and November precipitation can deliver a healthy dose of rain when tropical storms penetrate inland, but dry conditions typically characterize fall in the Southwest.  In the last 60 days, less than 0.5 inches of rain—less than 25 percent of average—has fallen in nearly all of Arizona and most of New Mexico (Figure 1).

The one exception has been in northern New Mexico, where a cold front sneaked into the region on November 5 and delivered precipitation. For most of the region, however, the percent of average metric can be misleading during this time of year because rain and snow accumulations are historically small. Consequently, drought conditions often remain fixed after the monsoon season until winter rain and snow begin—or do not begin—in earnest. Currently, severe drought covers about 25 percent of Arizona, while either severe or extreme drought exists over 38 percent of New Mexico. Drought in both states, however, is not as intense or widespread as it was one year ago.

The next several months will be pivotal for either improving or worsening drought conditions. Winter precipitation also substantially influences reservoir storage, because a large fraction of total annual streamflow in the region’s major rivers is generated from winter rain and snow. As of October 31, reservoirs in both Arizona and New Mexico were well-below capacity (see page 3). If recent snow in the Upper Colorado River and Rio Grande basins is a harbinger of things to come, the above-average snowpacks bode well (Figure 2).

A large storm set to slam the Southwest over the November 23 weekend could further build snowpacks and also improve short-term drought conditions. The seasonal precipitation outlook for December–February, however, favors below-average rain and snow for Arizona and New Mexico and equal chances for the Upper Colorado River and Rio Grande basins (Figure 3).

However, confidence in precipitation outlooks is lower in the absence of a La Niña or El Niño event. Historically, winters in which ENSO-neutral conditions prevail—the expectation this winter—have been characterized both by above- and below-average precipitation.