December 2010 Climate Summary
Drought– Nearly all of Arizona and New Mexico are classified with abnormally dry conditions or worse. In the last month, the percent of Arizona and New Mexico covered by drought ballooned from 49 and 31 percent, respectively, to about 95 percent in both states.
Temperature– Most of the Southwest has experienced temperatures between 0–4 degrees Fahrenheit above average in the last month. The Four Corners region and northeast New Mexico have experienced the largest temperature anomalies.
Precipitation– Precipitation in the last month has been scant across the Southwest. Most southern regions in Arizona and New Mexico have experienced less than 0.1 inches of rain, or less than 2 percent of average. Since the water year began on October 1, most of both states has received less than 50 percent of average precipitation.
ENSO– Below-average sea surface temperatures remain entrenched in the topical Pacific Ocean, and the moderate-to-strong La Niña event maintained its strength during the last month. There is an approximate 98 percent chance that La Niña conditions will continue during the December–February period although this is the time frame when La Niña events historically begin to wane.
Climate Forecasts– Nearly all of Arizona and New Mexico have elevated probabilities for warmer and drier conditions during the winter. Chances for drier conditions are highest—more than 50 percent—in southern parts of both states during the January–March and February–April periods.
The Bottom Line– The moderate-to-strong La Niña is helping to bring widespread abnormally dry conditions to most of the Southwest. La Niña events typically produce a more northerly winter jet stream pattern across the western U.S. which causes most storms to waft north of the southwest U.S. The most recent moderate La Niña event in 2007–08 produced a very dry January–March period in southern Arizona and southern and southeastern New Mexico. While La Niña has a strong drying effect in parts of the Southwest, the impact is not as strong in the Rocky Mountains in Colorado and Utah from which a large percentage of Colorado River water originates. Many monitoring sites in northern Colorado and Utah are currently reporting above-average snowpacks.