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Published December 19, 2011
Southwest Snowpack(updated 12/15/11)
Data Source(s): National Water and Climate Center, Western Regional Climate Center
Several wet and cold early winter storms have helped boost the amount of water contained in snowpack, or snow water equivalent (SWE), across the Southwest (Figure 8). SWE measured by snow telemetry (SNOTEL) stations in Arizona was all above 210 percent of average, with as much as 284 percent measured in the Central Mogollon Rim as of December 15. Snowpack in New Mexico has been slightly more variable, with southern mountains having more SWE than northern basins. SWE measured 331 percent of average in the Mimbres River Basin in southwest New Mexico and 88 percent in the Zuni-Bluewater River Basin in west-central New Mexico.
States to the north of Arizona and New Mexico, which supply most of the water to the Colorado River and Rio Grande, experienced a drier-than-average fall. The majority of SNOTEL stations in Colorado, Wyoming, and Utah measured less than 90 percent SWE as of December 15.
La Niña events usually deliver below-average rain and snow to the Southwest but do not as strongly influence precipitation totals in the Upper Colorado River Basin. Current forecasts issued by the NOAA-Climate Prediction Center (CPC) indicate a weak La Niña event will persist through the winter, increasing the odds of below-average rain and snow in Arizona, New Mexico, and southern Colorado. There are equal chances of above-, below-, or near-average precipitation for most of Utah, Wyoming, and parts of Colorado for the December–February and January–March periods (see page 14).
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
- Dan Ferguson, CLIMAS Program Director
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, CLIMAS Associate Staff Scientist
- Gigi Owen, CLIMAS Assistant Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Swetish, CLIMAS Publications Assistant
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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