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. Snow drought is a period of abnormally little snowpack for the time of year. Recent research shows that the western U.S. has emerged as a global snow drought “hotspot,” where snow droughts became more prevalent, intensified, and lengthened in the second half of the period 1980 to 2018.
Types of Snow Drought
There are two types of snow drought based on the AMS Glossary of Meteorology:
Dry snow drought
Below-normal cold-season precipitation
Warm snow drought
A lack of snow accumulation despite near-normal precipitation, caused by warm temperatures and precipitation falling as rain rather than snow or unusually early snowmelt.
Data, Maps, and Tools
Few drought metrics include storage and release of snow water. Several years of low snowpack, especially across the western U.S., have led to studies examining the causes and impacts of reduced snow storage and seeking a new definition for snow drought.
This USDA Natural Resources Conservation Service (NRCS) map shows Snow Telemetry (SNOTEL) snow water equivalent (SWE) basin values over the western U.S. as a percent of the NRCS 1981–2010 median. Only stations with at least 20 years of data are included in the station averages.
The SWE percent of normal represents the current snow water equivalent found at selected SNOTEL sites in or near the basin compared to the average value for those sites on this day. This map is valid as of July 18, 2021.
This map shows SNODAS snow water equivalent (SWE) values as a percent of normal. The SNOw Data Assimilation System (SNODAS) is a modeling and data assimilation system developed by NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) to provide the best possible estimates of snow cover and associated parameters to support hydrologic modeling and analysis. Learn more.
Snow Water Equivalent (SWE) Percent of NRCS 1981–2010 Median
SWE Percent of Normal (%)
Point maps and interactive maps of snow water equivalent, snow depth, and snow density from the Natural Resources Conservation Service (NRCS) Snow Telemetry (SNOTEL).
NOHRSC snow products include estimates of snow water equivalent, snow depth, snow pack temperatures, snow sublimation, snow evaporation, blowing snow, modeled and observed snow information, a
The CNAP Sierra Nevada Water Storage Tracker provides daily reservoir storage and snowpack information.
The Center for Western Weather and Water Extremes (CW3E) uses Global Ensemble Forecast System forecasts to show the evolution of the freezing level above, within, or below a watershed's terrain (th
Snow Today updates daily images on snow conditions and relevant data, and also provides monthly scientific analyses from January to May, or more frequently as conditions warrant.
Monthly streamflow maps comparing percent of monthly average flow to their respective 1981-2010 average. Available in spring and summer for the western U.S.
Impacts and Related Content
Summer Water Availability
Snow droughts reduce the amount of available water for spring and summer snow melt. This, in turn, reduces or shifts the timing of streamflow and reduces 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. This can create challenges for water management and flood mitigation strategies, particularly when dealing with extreme events.
By Sector | Recreation and Tourism
Many local economies and industries rely on snowpack and river flows from snowmelt to support their outdoor industries, such as skiing, rafting, and fishing.
Research & Learn | Snow Drought
Find more detailed information about snow drought, including the importance of snowpack and snow drought’s impact on ecosystems, water supply, and local economies.
The Great Western Snow Drought of 2015
The winter of 2015 brought unusually warm temperatures to the western United States and serves as a classic example of how warm temperatures can cause snow drought. By April 1, not a single basin in the West was above 86% of median snow water equivalent—and most basins in Washington, Oregon, California, Nevada, Utah, and Arizona were below 40%.
Snow Drought Research and Resources
The Climate CIRCulator: Snowpack & Drought Blog
The Climate CIRCulator: Snow Drought Declines in the American West
NASA Earth Observatory: Snow Drought in the Rockies
National Snow and Ice Data Center (NSIDC): Snow Today
2018 Western Snow Conference Videos
Story Map: Snow Drought in the 21st Century
Rocky Mountain West
Colorado’s Decision Support Systems SNODAS Tools
Snowpack Monitoring in the Rocky Mountain West: A User Guide (PDF)
Pacific Northwest
CIRC Pacific Northwest Snowpack, Hydrology, and Drought Resources
Seasonal Hydrologic Responses to Climate Change in the Pacific Northwest