Snowpack news

May 1, 2015 Colorado streamflow forecast map via the NRCS
May 1, 2015 Colorado streamflow forecast map via the NRCS

From the Leadville Herald Democrat:

Typically, by May 1 nearly all mountain snowpack measuring locations in Colorado are dominated by snowmelt opposed to snow accumulation, with the turning point or peak accumulation occurring slightly after April 1.

However, this year all basins experienced the turning point in early March with the exception of the South Platte, which due to mid-April storms, was able to achieve a snowpack peak this year close to normal.

When viewed from the Front Range, it may seem that recent precipitation has substantially increased the statewide year-to-date total (currently at 80 percent of normal), but the fact is that statewide April 2015 precipitation was only 71 percent of normal, while the South Platte April precipitation was 110 percent of normal. Mountain snowpack follows the same storyline; the South Platte snowpack is at 96 percent of normal on May 1, while statewide snowpack is just 61 percent of normal. The Rio Grande snowpack is the lowest in the state at 25 percent of normal on May 1.

“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 Natural Resources Conservation Services Colorado Snow Survey Program. During the snowmelt season, when attempting to get a better understanding of water supply for the remainder of the water year, it is important to remember that snowpack is not the only factor involved in spring and summer runoff. Other factors to consider include snowpack peak timing and spring rain.

Snowpack peak timing, which occurred early this year, 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 does not add to the snowpack, but often augments streamflow. Largely that rain has not come to Colorado.

These factors and many others, Domonkos goes on to say, “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 currently below average. However, without abundant rain, streamflow outlooks will likely not improve enough to make a substantial difference in the entire water budget.

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