Home » August 2011 Southwest Climate Outlook » August 2011 Southwest Climate Outlook
Published August 23, 2011
Photo of Lightning during Monsoon season

Source: John Capuano

The monsoon brought its own impressive July 4 display with a lightning show in Tucson, AZ.

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.

News Flash: Big Snowpacks Boon for Colorado River Reservoirs

Most La Niña events have not delivered as much snow to the Rocky Mountains as the one did last winter. It was a welcome windfall for the Colorado River, which provides water for nearly 30 million people in seven states and Mexico. At the onset of winter, things were looking grim. Lake Powell was at 63 percent of capacity, while the water level in Lake Mead was only six feet above a trigger point for water conservation—a record low. In the last decade, Lake Mead’s elevation plunged nearly 100 feet as enduring drought gripped the Colorado River Basin.

In recent months, however, Lake Powell has risen by more than 40 feet, peaking at a 10-year high in July at 76 percent of capacity (Los Angeles Times, August 13). Lake Mead also has risen by about 30 feet and is expected to continue to climb by about another 40 feet during the next year and a half as water from Powell is released into Lake Mead to fulfill obligations established in the Colorado River Compact. While many researchers and water managers expect the joint effects of high demand and climate changes to trigger water conservation measures at some point soon, some estimates now suggest that date may not be reached until at least 2014 (Las Vegas Sun, August 17).