Forecasts and Outlooks > Archive
Southwest Climate Outlook - July 2003

Date issued: July 25, 2003

A. Summary

Hydrological drought will continue to be a major concern for the Southwest during the upcoming months. Most New Mexico river basins remain in emergency drought status. Current storage has continued to decrease in many Arizona reservoirs.

Summer monsoon rainfall has arrived in parts of the Southwest. The monsoon arrived late, bringing lower than average precipitation thus far. On average, late monsoons bring lower than average summer total precipitation.

Fire danger is above average across all of Arizona and western New Mexico, especially at elevations lower than 8,500 feet. However, the arrival of summer monsoon rainfall will ease fire danger.

New Mexico and Arizona continue to have the poorest range and pasture conditions (relative to state averages) in the United States.

Seasonal temperature forecasts indicate increased probabilities of above-average temperatures across Arizona and New Mexico until at least the end of 2003.

Sea surface temperatures have increased in the central equatorial Pacific Ocean and ENSO conditions are now neutral. The chances of La Niña developing by the end of the year are less than 50%.

Bottom line: Hydrological drought will continue in the Southwest during the next several months.

The most likely scenario is that summer rainfall will be near average. Summer rainfall tends to have minimal impact on reservoirs. Range and pasture conditions might benefit in some areas, most likely in the southern part of our region and in northern Mexico. Neutral-to-slightly cool (weak La Niña) equatorial Pacific Ocean temperatures will persist beyond the summer, resulting in slightly increased chances of below-average autumn precipitation. Enhanced erosion following fires is a concern during the summer.

The worst case scenario is that summer monsoon precipitation is lower than average during a period when above-average temperatures persist. The aforementioned scenario will result in persistent extreme fire danger, high evaporation rates, and decreased reservoir and groundwater levels. CLIMAS research shows that summer rainfall has seldom ended severe sustained drought (see END InSight Newsletter, August 2002).

The best case scenario is that in the short-term the Southwest will receive abundant and regular summer rainfall. Fire danger will ease, although the chances of severe erosion will be increased by monsoon storms. In the long term, the best-case scenario is for neutral central and eastern Pacific Ocean temperature conditions to persist or for El Niño conditions to rebound later this year. The aforementioned scenario will increase the chances of above-average fall and winter precipitation. Reservoir and groundwater levels will be maintained at current levels or increase.

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