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Snow Drought

What is Snow Drought?

Snow drought is defined as period of abnormally low snowpack for the time of year, reflecting either below-normal cold-season precipitation (dry snow drought) or a lack of snow accumulation despite near-normal precipitation (warm snow drought), caused by warm temperatures and  precipitation falling as rain rather than snow or unusually early snowmelt. (AMS Glossary of Meteorology)

Current situation and impacts in the West

May 10, 2018:
Early May is well into the snowmelt season in the Western US. Cold late season storms can bring snowfall, but tend to slow the melt process rather than build the snowpack. Currently, snowpack remains well below normal in southern Oregon, California, southern Idaho, Utah, southern Colorado, and northern New Mexico. Many sites in these regions are at less than 25% of normal, and many lower elevation sites have already melted out with no snowpack remaining. A sharp contrast is found to the north in Washington and the northern Rockies where most sites have well above normal snowpack. In Central Alaska snowpack is above normal while most sites in the Kenai Peninsula and Chugach Mountains in the southern part of the state are below normal. [Next update scheduled for May 24, 2018]
 

A map of the United States, focusing in on the Western US and a second map of Alaska, shows the percent of 1981-2010 median snow water equivalent (SWE) based on SNOTEL site data from the United States Department of Agriculture Natural Resources Conservation Service for May 7, 2018. The SWE percent of 1981-2010 median values is displayed using a range from <0 to >200%. Most of the California Sierra Nevada mountains are well below normal, generally ranging from <0% to 75% with a few sites nearer to 100% of median. The same is true for the southern Cascade Range and Blue Mountains in Oregon with 100->200% in the Washington Cascades. The northern Rockies through Wyoming and Montana have above median SWE, ranging from 100 to >200%. Meanwhile the Colorado River Basin and the southern Rockies into the Four Corners region are below to well below median, ranging from <0% to 100%. Snowpack is well below median values in southern and southeastern Nevada, reaching as low as 0-25%. A map focusing in on Alaska, showing the percent of 1981-2010 median snow water equivalent (SWE) based on SNOTEL site data from the United States Department of Agriculture Natural Resources Conservation Service for May 7, 2018. Most of central Alaska is above median snowpack, with values ranging from 150 to >200% while parts of south and southeastern Alaska are more near or below normal.

USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 median snow water equivalent (SWE) over the western U.S. (left/top) and Alaska (right/bottom) for May 7, 2018. Only stations with at least 20-years of data are shown. For an interactive version of this map, including percent of period of station record median SWE, please visit NRCS

One graph displays daily SNOTEL snow water equivalent (SWE) for the San Miguel, Dolores, Animas and San Juan River basins in southwest Colorado. On the x-axis is the water year from Oct 1, 2017 to Sept 30, 2018 and on the y-axis is daily SWE in inches. A black line on each graphs the 2018 SWE values through May 8, 2018. A light red line shows the 1981-2010 average and a dark red line shows the median. A green line shows 2015, a yellow line shows 2016, and a blue line shows 2017. The region is currently well below normal with SWE at 15% of normal (median).

SNOTEL basin-wide average SWE time series for the San Miguel, Dolores, Animas and San Juan River basins in southwest Colorado. Black line is this year, lighter red line is the average, and darker red line is the median. The region peaked in late March at 52% of normal peak SWE, and is currently at only 15% of normal SWE for this date.

 

A map of the United States, focusing in on the Western US, shows the SNOw Data Assimilation System (SNODAS) percent of average (2004-2018) snow water equivalent (SWE) for May  6, 2018. The SWE percent of average is displayed using a ranging from 0 to 800%. Most of the California Sierra Nevada mountains are below average generally ranging from 5-130% of normal. The same is true for the southern Cascade Range and Blue Mountains in Oregon with above average (some areas >200%) in the Washington Cascades. The northern Rockies through Wyoming and Montana have above average SWE, in some places as high as 200%-400% of average. Meanwhile the Colorado River Basin and the southern Rockies are near or below average. The northern Bitterroot Range in Idaho is near average. Finally, much western Montana is still well above average.

SNOw Data Assimilation System (SNODAS) percent of average (2004-2018) snow water equivalent (SWE) for May 6, 2018. Image made using Climate Engine. Please note the shorter historical period of this dataset compared to the station data above.

 

Snow Drought Tools