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Published April 25, 2012
Southwest Snowpack(data through 4/19/12)
Data Source(s): National Water and Climate Center, Western Regional Climate Center
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.Notes:
Snowpack telemetry (SNOTEL) sites are automated stations that measure snowpack depth, temperature, precipitation, soil moisture content, and soil saturation. A parameter called snow water equivalent (SWE) is calculated from this information. SWE refers to the depth of water that would result by melting the snowpack at the SNOTEL site and is important in estimating runoff and streamflow. It depends mainly on the density of the snow. Given two snow samples of the same depth, heavy, wet snow will yield a greater SWE than light, powdery snow.
This figure shows the SWE for selected river basins, based on SNOTEL sites in or near the basins, compared to the 1971–2000 average values. The number of SNOTEL sites varies by basin. Basins with more than one site are represented as an average of the sites. Individual sites do not always report data due to lack of snow or instrument error. CLIMAS generates this figure using daily SWE measurements made by the Natural Resources Conservation Service.
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer