Monsoon Summary

Vigorous monsoon activity in many parts of the Southwest during late July and early August has helped make up for a dry start to the season and has helped alleviate drought conditions in many parts of both Arizona and New Mexico. Since mid-July, northern and eastern Arizona and northwestern New Mexico have received more than 150 percent of average rainfall (Figure 9a). In Payson, Arizona, July storms dumped a record-setting 3.8 inches of rain, according to the National Weather Service. Only southwestern Arizona and southern New Mexico have experienced dry conditions. Since the monsoon officially began on June 15 in Arizona (New Mexico does not have an official start date), precipitation totals have been between 2 and 6 inches in most of Arizona, and 2 and 10 inches in New Mexico (Figure 9b). Rain storms in the last month have boosted rainfall totals to above-average levels in the eastern portion of Arizona and many parts of New Mexico (Figure 9c). Despite copious rains in many regions, the Colorado River corridor in western Arizona, and particularly in southwest Arizona, has been parched. Many areas in this section have seen less than 5 percent of average rainfall.

The remainder of the monsoon season is more likely to be dry in northern regions of Arizona. The NOAA–Climate Prediction Center’s (CPC) September precipitation forecast calls for drier conditions in the northern regions, while the forecast calls for equal chances of below-, above-, or near-average rainfall in southern portions of the Southwest. The CPC seasonal forecast for the September–November period calls for drier-than-average conditions in all areas of Arizona and New Mexico. The dominant influence on these forecasts is the La Niña event that has taken hold in the tropical Pacific Ocean and is expected to strengthen and continue into 2011. La Niña events often cause winter storm tracks to waft north of the Southwest.