What is Snow Drought?

Snowpack typically acts as a natural reservoir, providing water throughout the drier summer months. Lack of snowpack storage, or a shift in timing of snowmelt from that reservoir, can be a challenge for drought planning. Few drought metrics include storage and release of snow water. Several years of low snowpack, especially across the western U.S., have led to many studies looking into the causes and impacts of reduced snow storage (see Resources) and the creation of a new definition of drought called 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)

Snow-dominated regions face several challenges due to snow drought and its impacts:

• Summer Water Availability: Snow droughts reduce the amount of available water for spring and summer snow melt. This, in turn, reduces streamflow and soil moisture, which can have impacts on water storage, irrigation, fisheries, vegetation, municipal water supplies, and wildfire.

• Winter Water Management: Warmer winter storms lead to rain instead of snow at higher elevations in mountain regions that can create challenges for water management and flood mitigation strategies, particularly when dealing with extreme events.

• Outdoor Tourism and Recreation: Many local economies and industries rely on snowpack and river flows from snowmelt to support their outdoor industries such as skiing, rafting, and fishing.

• Ecosystems: Lack of snow can disrupt ecosystems over shorter and longer timescales.

Current Situation and Impacts in the West

March 21, 2019: 
Currently only small areas of snow drought are present in the western contiguous U.S. after a wet winter (December-February) with Washington and Wyoming being the only two western states to have below normal winter precipitation. Washington, northern Idaho, northwest Montana, and the Bighorn Mountains of northern Wyoming are the only places that currently have widespread below normal snow water equivalent (SWE). Still, the deficits are relatively small at the large river basin scale with the Puget Sound Basin in western Washington currently reporting the lowest SWE in the west at 83% of median. Conversely, many of the basins in California, Nevada, Utah, and Colorado are currently greater than 150% of median with the Lower Sacramento, San Joaquin, Truckee, Carson, and Walker River Basins in the Sierra Nevada all above 170% of median SWE. Below normal SWE has persisted for much of the year in the mountains of southern Alaska due to early season warm snow drought and mid-season dry snow drought including the Knik Arm, Prince William Sound, and Kenai Peninsula Basins. Snowpack was near to above normal on the south slopes of the Alaska Range and much above normal in the northern and western Interior. A recent series of storms beginning on March 8 has brought substantial snow and modest improvements to the snow drought conditions on the Kenai Peninsula and Prince William Sound area. The Turnagain Pass SNOTEL gained 7.6 inches of SWE between March 8-18 and a snow depth change of 38 inches, and a change from 59% of median SWE to 78%.