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Published April 27, 2011
Southwest Snowpack(updated 4/20/11)
Data Source(s): National Water and Climate Center, Western Regional Climate Center
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.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 content (SWC) or snow water equivalent (SWE) is calculated from this information. SWC 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 SWC than light, powdery snow.
This figure shows the SWC 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 SWC measurements made by the Natural Resource 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.
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