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Published April 24, 2013
Southwest Snowpack(data through 4/18/13)
Data Source(s): National Water and Climate Center, Western Regional Climate Center
A recent storm in the northern sections of the Upper Colorado River Basin helped restock snowpacks there, but precipitation was below average in the southern half of Utah and Colorado and in all of Arizona and New Mexico in the past 30 days. Dry conditions in Arizona and New Mexico, however, are the norm for this time of year.
Despite the recent snow, water contained in snowpacks, or snow water equivalent (SWE), is below average in most basins (Figure 8). In the Upper Colorado River Basin, snow telemetry (SNOTEL) monitoring stations mostly report that total winter precipitation has been less than 90 percent of average, which is an increase from one month ago. In the headwaters of the Rio Grande in Colorado, the average of 12 SNOTEL stations report 66 percent of average SWE, with the total winter precipitation measuring only 69 percent of average. Below-average precipitation, consequently, is driving low streamflow forecasts for these rivers. The best estimates for spring streamflows in the Rio Grande and Colorado River are less than 50 percent of average. The Colorado River may also experience its fourth lowest April–July streamflow since Lake Powell became operational in 1963.
In the Mogollon Rim region of Arizona, SNOTEL monitoring sites have recorded near-average precipitation, but the current SWE values are less than 5 percent of average. Numerous days of much above-average temperatures in mid-March helped rapidly melt these snowpacks, as well as those in many other regions in Arizona. The only exception to below-average SWE in Arizona is in the upper Salt River Basin in the White Mountains, where recent snows helped boost snowpacks there. For Arizona and New Mexico, low SWE values in mid-April suggest that the landscape may desiccate sooner than average, which, in turn, would elevate fire risk in these areas. Also, SWE values in April are not as good an indicator of water supply as total accumulated precipitation because even small snowfall amounts can greatly boost the percent of SWE.
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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