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Published March 27, 2013
Southwest Snowpack(data through 3/21/13)
Data Source(s): National Water and Climate Center, Western Regional Climate Center
Precipitation in the last month has been below average in many parts of the higher elevations in Arizona, New Mexico, Colorado, and Utah. Temperatures also have been above average in these states. The combination of the two has caused water contained in snowpacks, or snow water equivalent (SWE), to be below average in many basins (Figure 8). In the Upper Colorado River Basin, snow telemetry (SNOTEL) monitoring stations largely report SWE values of less than 80 percent of average. In these basins, the total accumulated winter precipitation also has been about 80 percent of average. In the headwaters of the Rio Grande in Colorado, the average of seven SNOTEL stations report 72 percent of average SWE. Consequently, the scant snowfall this winter is driving below-average streamflow forecasts for these rivers; best estimates for spring streamflows in the Rio Grande and Colorado River are around 50 percent of average.
In Arizona, despite near-average total winter precipitation in the Verde River Basin, the central Mogollon Mountains, and headwaters of the Little Colorado River, current SWE values in these regions are 52, 60, and 60 percent of average, respectively. This likely reflects the very warm recent conditions that have depleted once near-average snowpacks. Incursions of warm temperatures, or an earlier onset of spring, can explain why much below-average SWE can occur amid a winter of near-average total accumulated precipitation. In the past two weeks, for example, average temperatures in Arizona have largely been 3–4 degrees F above average. Warmer-than-average temperatures also have been the norm in Colorado in recent weeks. However, because elevations are higher in Colorado, average temperatures are lower and snowpack conditions remain similar to total accumulated winter precipitation.
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.
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