Southwest Snowpack

Below-average precipitation and warming temperatures across most of the Southwest in the last month have precipitated decreases in the amount of mountain snow. In Arizona, the water contained in snowpacks, or snow water equivalent (SWE), measured by snow telemetry (SNOTEL) stations was less than 15 percent of average in all but the San Francisco Peaks, where SWE was 49 percent of average as of April 19 (Figure 8). The Upper Salt River and the Verde River basins measured only 7 and 11 percent of average, respectively, a decline from 40 and 20 percent reported last month.

In New Mexico, all basins reported in Figure 8 had well below-average snowpacks. Whereas most basins reported snowpacks greater than 70 percent of the 1971–2000 average last month, currently all but one basin reported values equal to or less than 45 percent of average. Some basins are reporting no snow, including the San Francisco and the Gila river basins in the southwest corner of the state and the Jemez River Basin in northern New Mexico. The Pecos and Animas river basins reported the highest SWE, measuring 55 and 45 percent, respectively. The below-average snowpacks are in part caused by recent warm temperatures. Temperatures across most of the state ranged from 2 to 6 degrees F above average in the last month.

All monitoring stations in Colorado and Utah also reported well below-average SWE as of April 19. As a result, streamflow forecasts for the Upper Colorado River Basin are below average; inflow into Lake Powell, for example, has a 50 percent chance of being less than 3.5 million acre-feet, or 44 percent of the historical average, for the April–July period.