Home » April 2011 Southwest Climate Outlook
Published April 27, 2011
A solitary native cactus bee gathers pollen and nectar from a prickly pear flow

Photo Description: A solitary native cactus bee gathers pollen and nectar from a prickly pear  flower in the cactus garden on the University of Arizona Mall.

Source: Walter Freeman, UA Graduate Student Physics.

April Climate Summary

Drought– Unusually dry weather over the past 30 days has caused short-term drought conditions to continue to expand and increase in severity across much of New Mexico and Arizona, particularly southern regions of both states.

Temperature– Temperatures across the Southwest have been hotter than average in the past 30 days, with most of New Mexico and southeastern Arizona experiencing temperatures more than two degrees warmer than average.

Precipitation– Scant precipitation fell during the winter in most of the Southwest—New Mexico experienced its 6th driest winter of the last 116. That pattern has been upheld in the past 30 days—virtually no precipitation fell in most of New Mexico, while Arizona experienced patches of wetter- and drier-than-average conditions.

ENSO– The La Niña of 2010-11 is coming to an end, with sea-surface temperatures in the equatorial Pacific quickly warming to near-average levels for this time of year. ENSO-neutral conditions are expected to return by early summer.

Climate Forecasts– Forecasts call for a greater than 50 percent chance that temperatures will be above average through the spring and early summer. Equal chances of above-, below-, or near-average rainfall are projected through the summer.

The Bottom Line–La Niña was the headline of the winter, causing extremely dry conditions in Arizona and New Mexico. Precipitation in many southern parts of both states measured less than 25 percent of the historical average since October 1. January 2011 was the driest on record for New Mexico, and the October–March season was the sixth driest. Snowpacks were also low. However, not all the news is bad. A wet winter in the Upper Colorado Basin is fueling an above-average spring streamflow forecast for the Upper Colorado River, which will help boost storage in lakes Mead and Powell. With the upcoming months historically dry and warm in Arizona and New Mexico, the onus will be on the monsoon to deliver rain and stave the expanding and intensifying drought conditions: 12 and 33 percent of Arizona and New Mexico, respectively, are classified with extreme drought conditions.  The dry winter combined with forecasts of continued parched conditions and warmer-than-average temperatures also are fanning an increased risk for wildland fires.

News Flash: Lake Mead Levels to Rise

The surface of Lake Mead is expected to rise almost 20 feet over the next 10 months, reaching an elevation of about 1,105 feet above sea level by the end of September, according to a Bureau of Reclamation (BOR) press release (April 12). A total of 11.23 million acre-feet of water will flow into Lake Mead this year in part because copious winter snows in the Upper Colorado River Basin have helped elevate spring streamflow forecasts to about 120 percent of average. The wet winter, however, is not the whole reason for increasing storage in Lake Mead. Water managers devised a set of rules for various scenarios outlined in the 2007 Environmental Impact Statement that provide guidelines for managing the basin under drought conditions. Under the rules for 2011 operations, if Lake Powell water elevation is at or above 3,643 feet above sea level and the September 30 projected Lake Mead elevation is below 1,105 feet, BOR must release additional water from Lake Powell to Lake Mead until either the reservoir storages are equal, Lake Mead reaches an elevation of 1,105 feet, or Lake Powell elevation declines by 20 feet below 3,643. These rules also apply for the following years, with slight yearly increases to the 3,643 threshold water elevation for Lake Powell.