Colorado’s early peak snowpack, light precipitation mean low streamflows
April precipitation statewide underperformed, according to the monthly update released May 8 by the Natural Resource Conservation Service.
The report doesn’t include data from the latest storm, which bumped snowpack in Summit County’s Blue River Basin to above-average for this time of year and brought about 12 inches of snow to Arapahoe Basin Ski Area.
Typically, by May 1 nearly all mountain snowpack measuring locations in Colorado are dominated by snowmelt opposed to snow accumulation, with peak accumulation occurring slightly after April 1.
However, this year all basins experienced that turning point in early March with the exception of the South Platte, which was able to achieve a snowpack peak this year close to normal due to mid-April storms.
Statewide April 2015 precipitation was 71 percent of normal, while the South Platte April precipitation was 110 percent of normal.
Snowpack follows the same storyline. The South Platte snowpack was at 96 percent of normal on May 1, while statewide snowpack was 61 percent of normal.
The Rio Grande snowpack was the lowest in the state at 25 percent of normal.
“Statewide snowpack peaked during mid- to early March at about 75 percent of the normal peak snowpack. This means that mountain snowpack this year will only provide about three-quarters of the typical snowmelt to contribute to streamflow,” said Brian Domonkos, hydrologist with the USDA NRCS Colorado Snow Survey Program.
People should remember, he noted, that snowpack is not the only factor involved in spring and summer runoff when attempting to get a better understanding of water supply. Other factors to consider include snowpack peak timing and spring rain.
An early snowpack peak timing often results in poor runoff efficiency.
Monthly precipitation has been well below normal in nearly every basin for the last two months, which carries more weight since March (63 percent of normal) and April are the two months of the year in which Colorado typically receives the most precipitation.
Additionally, April often provides rain at the lower elevations, which amplifies streamflow, and largely that rain has not come to Colorado.
These factors, Domonkos added, “paint a poor streamflow forecast picture for much of the state heading into spring and summer of 2015.”
Future near- or above-normal precipitation would improve streamflow prospects in most watersheds that are below average, but without abundant rain, streamflow outlooks will likely not improve enough to make a substantial difference.
For more information about Colorado’s snowpack or water supply, go to the Colorado Snow Survey website at http://www.nrcs.usda.gov/wps/portal/nrcs/main/co/snow/ or contact Brian Domonkos, Colorado snow survey supervisor, at Brian.Domonkos@mt.usda.gov or 720-544-2852.
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