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
April 4, 2019:
Active weather continued for the last two weeks of March into the beginning of April across central and northern California, the Great Basin, and Utah where above normal precipitation fell and an already deep snowpack continued to increase. A dry pattern remained in place for the North Cascades of Washington where snow drought conditions have become more severe. The Puget Sound Basin in northwest Washington received only 14% of average precipitation for the period of March 19 through April 1 and currently sits at 73% of median snow water equivalent (SWE). In northern Idaho, northwest Montana, and parts of north-central Wyoming SWE is also currently below normal. Some of the worst snow conditions are currently in the Big Horn Mountains in northern Wyoming with most stations at 70%-85% of median SWE. Burgess Junction, Wyoming (elevation 7880’) and Dome Lake, Wyoming ( elevation 8880’) stations are both reporting the lowest SWE on record for April 1 dating back to 1979 and 1978, respectively. Overall, snow drought conditions in Alaska have remained largely unchanged over the past two weeks with continued below normal SWE in southern coastal ranges and interior ranges near Fairbanks. After a series of strong storms in mid-March around the Kenai Peninsula and Prince William Sound area boosted SWE, warm and dry weather has returned leading to substantial SWE decreases at lower elevation locations. At Summit Creek, Alaska (elevation 1400’) SWE dropped from 9 inches on March 22 to 5.7 inches on April 2 leaving the station at 51% of median.
USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 median snow water equivalent (SWE) over the western U.S. (top) and Alaska (bottom) for March 31, 2019. Only stations with at least 20-years of data are included in the station averages. For an interactive version of this map, including percent of period of station record median SWE, please visit NRCS.
USDA Natural Resources Conservation Service (NRCS) SNOTEL site daily (inches) water year accumulated precipitation (black line) and SWE (blue line) plotted with long term median precipitation (grey line) and SWE (red line) at Summit Creek, Alaska. Between March 22 and April 2 the snow water equivalent decreased 3.3 inches, and the April 2 SWE was at 51% of median. Source: NRCS