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Western U.S. Snowpack Melting At Record Speed
The U.S. Department of Agriculture's Natural Resources Conservation Service issued its final "west-wide forecast" of the season this week. It shows that snowpack, from Washington to Wyoming, is melting so quickly, flooding is a possibility in some areas.
"Most areas saw major decreases in snowpack during April and are now below normal," according to the NRCS May 2016 Western Snowpack and Water Supply Conditions report.
"The notable exceptions to this that still have above normal snowpack include the Rocky Mountains of northern Colorado and western Wyoming, while the central Sierra in California remains near normal. Elsewhere, snow is generally well below normal or completely melted out."
The report says that snowpack in Alaska "is now well below normal throughout the state."
"In the Pacific Northwest, low precipitation and high temperatures led to a dramatic reduction in snowpack," says NRCS Hydrologist Cara McCarthy. "In this area, peak streamflow is arriving weeks earlier than normal this year."
But McCarthy says not all areas in the west have low snowpack.
"Parts of Wyoming and Colorado have seen much above-average precipitation in recent weeks, causing concerns about potential flooding in the North Platte," she says.
May is the last "West-wide" forecast of the season, but NRCS will continue monitoring conditions throughout the year. As of May 6, the statewide snowpack in the Sierra Nevada was 57 percent of normal.
"In Western states where snowmelt accounts for the majority of seasonal water supply, information about snowpack serves as an indicator of future water availability," the NRCS says in a May 6 news release. "The wildland fire community closely watches snowpack and water supply availability predictions as limited snowpack and the rate of snowmelt are two of the many factors that affect the potential severity of the wildland fire season in the West.
"Streamflow in the West consists largely of accumulated mountain snowmelt that flows into streams as temperatures warm in spring and summer. NRCS scientists analyze the snowpack, precipitation, air temperature and other measurements taken from remote sites to develop the water supply forecasts."
The NRCS says it uses the water supply forecast, issued monthly from January to May, "to improve public awareness and manage the impacts of climate change, including drought and other extreme weather events."
The snowpack report comes as the drought in California continues for a fifth consecutive year. While conditions were near-normal in the northern Sierra Nevada over the winter, snowpack in the central and southern Sierra were less bountiful.
California's largest reservoirs, Shasta and Oroville, benefitted from the ample snowfall in winter 2015-16, and that water will be tapped to supply farms and urban areas through the summer.
But, despite the forecast of a "Godzilla" El Niño throughout California, most of the heavy precipitation was in northern, not southern California.
The north-south split in precipitation over the winter added snowpack to the northern Sierra and helped reservoirs in the north.
NOAA reported May 6 that the January through April 2016 contiguous U.S. average temperature was 43.1°F – 4.0°F above average. California, Nevada, Oregon and Washington were among the states with normal temperatures "much above average" so far this year.
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