Southwest Snowpack

The volume of water contained in snowpacks, or snow-water equivalent (SWE), across Arizona and New Mexico was below average  at almost every snow Telemetry (SNOTEL)  as of April 21 (Figure 8). An early April storm boosted snowpacks and precipitation totals in many parts of the Southwest, but most of that snow has melted. Prior to the storm, snow was scant in most of the high country in central and southern Arizona and New Mexico (see last month’s Snowpack Summary). The warmer-than-average temperatures predicted for the upcoming month will cause continued and rapid melting. Overall, the October through mid-April SWE for all basins in Arizona was below average, as was the combined basin average for the Salt and Verde river systems.

The moderate-to-strong La Niña event is largely to blame for the dry conditions in the Southwest. However, it also helped deliver above-average snows to the Upper Colorado River Basin states of Utah, Colorado, and Wyoming, from which about 80 percent of the water in the Colorado River originates. As a result, spring streamflow forecasts for Lake Powell predict a 50-percent chance that inflow into the reservoir will be about 120 percent of the 1971–2000 average. Spring streamflow forecasts for other Arizona and New Mexico rivers all call for below-average discharge, with some rivers likely to flow at less than 50 percent of average. Forecasts for the Rio Grande, for example, indicate a 50-percent chance that streamflow at Otowi Bridge will be only 48 percent of average for the April–July period.