Southwest Climate Outlook August 2011

Date issued

August 2011 Climate Summary

Drought– Exceptional drought declined slightly in Arizona and New Mexico in the last month. However, monsoon rains generally have been below average and drought conditions are still widespread and intense in most of the region.

Temperature–A strong high pressure ridge has left New Mexico with extremely warm temperatures that have been between 2 and 8 degrees Fahrenheit above average in the last month. In Arizona, temperatures have been generally 0–4 degrees F above average.

Precipitation– The monsoon delivered above-average rain to southeastern Arizona in the last month; below-average rain still characterizes the monsoon season for most of the rest of Arizona and New Mexico.

ENSO– ENSO-neutral conditions are still present across the equatorial Pacific Ocean, but signs are mounting that weak La Niña conditions may return as early as this fall.

Climate Forecasts– Forecasts call for increased chances for above-average temperatures and below-average rainfall during the September–November period for most of Arizona and New Mexico. These forecasts are based in part on recent conditions and trends.

The Bottom Line–With much of the monsoon season now over, constant and copious rains have not yet materialized for most of the region. Only the southeastern and southwestern corners of Arizona and New Mexico, respectively, have experienced above-average rainfall. A more easterly position of the monsoon ridge, which has helped block moisture from New Mexico, and weak winds aloft, which have prevented storms from moving off the mountains and into the valleys, are partly to blame for the drier-than-average monsoon season. As a result, about 77 percent of New Mexico and 12 percent of Arizona are classified with exceptional and extreme drought, respectively. Relief does not appear to be on the horizon. Forecast models call for slightly increased chances for below-average rain in September. Also, forecasters have been increasing the odds that La Niña will return this winter—currently, there’s a 44 percent chance that La Niña will develop and a 54 percent chance that neutral conditions will persist during November-January. A back-to-back La Niña event would likely intensify and spread drought to the region. Next month should provide a more definite picture of whether the winter will be influenced by La Niña.

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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