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
December 13, 2018:
A series of storms from late November through early December brought beneficial rain and mountain snow to California, Nevada, and Utah where most stations are now reporting above normal snow water equivalent. Oregon, Washington, northern Idaho, and northwest Montana remain in snow drought. Above normal temperatures have impacted snow accumulation in the northern Cascades of Washington where water year-to-date precipitation is only near-to-slightly below normal with snow deficits well below normal. Much of Colorado continues to build a healthy, above normal snowpack with the exception of the southwest portion of the state. The Upper San Juan drainage basin currently sits at 63% of median snow water equivalent. Most of central and southern Alaska are experiencing warm snow drought with current snow water equivalent about 30-60% of the 1981-2010 median while water year-to-date precipitation is well above normal. An example of such warm snow drought conditions is the Kenai Peninsula drainage basin where snow water equivalent is currently 38% of median and water year-to-date precipitation is 167% of average.
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 December 9, 2018. 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