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Snow Drought

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

February 7, 2019:
Mid-winter snowpack is near or above normal in a belt across the middle latitudes of the western US including the Sierra Nevada, Great Basin, Utah, and Colorado. After a good start to the winter, storms with warmer temperatures and higher snow levels have led to a rapid decline of snowpack in the mountains of central Arizona and southwest New Mexico creating warm snow drought conditions. For example, the Salt River Basin in central Arizona currently sits at 71% of median snow water equivalent despite accumulated water year precipitation being at 95% of median. The other area of snow drought in the lower 48 includes western Washington and Oregon. These areas are also in a warm snow drought although precipitation has also been below normal. In Oregon’s Willamette Basin, conditions are currently at 56% of median snow water equivalent and accumulated water year precipitation is at 79% of median. Throughout northwest Wyoming, Idaho, and western Montana conditions are mixed with pockets of above and below normal snowpack present. Nearly all stations south of the Arctic Circle in Alaska currently have below normal snowpack. This has been driven by a lack of precipitation in the Interior and southeast Alaska while the southern basins including Prince William Sound, Kenai Peninsula, Knik Arm, and Susitna River all have above normal water year precipitation indicating warm snow drought conditions.

Two panels show 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 February 3, 2019. Only stations with at least 20-years of data are included in the station averages. In the top panel a map of the Western US show mid-winter snowpack is near or above normal in a belt across the middle latitudes of the western US including the Sierra Nevada, Great Basin, Utah, and Colorado. Areas with below average SWE include central Arizona, southwest New Mexico, Washington and Oregon including some stations showing <25% of average. In the lower panel displaying Alaska, nearly all stations south of the Arctic Circle in Alaska are below normal for snowpack with above normal water year precipitation and warm snow drought conditions.Two panels show 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 February 3, 2019. Only stations with at least 20-years of data are included in the station averages. In the top panel a map of the Western US show mid-winter snowpack is near or above normal in a belt across the middle latitudes of the western US including the Sierra Nevada, Great Basin, Utah, and Colorado. Areas with below average SWE include central Arizona, southwest New Mexico, Washington and Oregon including some stations showing <25% of average. In the lower panel displaying Alaska, nearly all stations south of the Arctic Circle in Alaska are below normal for snowpack with above normal water year precipitation and warm snow drought conditions.

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 February 3, 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 stations in the Oregon (top) and Washington (bottom) Cascades on February 4, 2019. Percent of 1981-2010 median snow water equivalent (SWE) is plotted on the horizontal axis against station elevation on the vertical axis. Dots are colored by accumulated water year precipitation percent of 1981-2010 average. Warm snow drought is easy to identify by the strong increase in SWE with elevation driven by warm temperatures and rain at lower elevations for much of the winter. In the Washington Cascades (bottom) five stations, all below 1200 m elevation, currently are below 40% of median SWE with 80-120% of average water precipitation. USDA Natural Resources Conservation Service (NRCS) SNOTEL stations in the Oregon (top) and Washington (bottom) Cascades on February 4, 2019. Percent of 1981-2010 median snow water equivalent (SWE) is plotted on the horizontal axis against station elevation on the vertical axis. Dots are colored by accumulated water year precipitation percent of 1981-2010 average. Warm snow drought is easy to identify by the strong increase in SWE with elevation driven by warm temperatures and rain at lower elevations for much of the winter. In the Washington Cascades (bottom) five stations, all below 1200 m elevation, currently are below 40% of median SWE with 80-120% of average water precipitation.

USDA Natural Resources Conservation Service (NRCS) SNOTEL stations in the Oregon (top) and Washington (bottom) Cascades on February 4, 2019. Percent of 1981-2010 median snow water equivalent (SWE) is plotted on the horizontal axis against station elevation on the vertical axis. Dots are colored by accumulated water year precipitation percent of 1981-2010 average. Warm snow drought is easy to identify by the strong increase in SWE with elevation driven by warm temperatures and rain at lower elevations for much of the winter. In the Washington Cascades (bottom) five stations, all below 1200 m elevation, currently are below 40% of median SWE with 80-120% of average water precipitation.

 

 

Snow Drought Tools

Example image of a NRCS SNOTEL and Snow Course Data
Point maps and interactive maps of snow water equivalent, snow depth, and snow density from the Natural Resources Conservation Service (NRCS) Snow Telemetry (SNOTEL).
Example image of a Climate Engine SNODAS image showing snow water equivalent
Climate Engine uses Google’s Earth Engine for on-demand processing of satellite and climate data via a web browser. Click for SNOw Data Assimilation System (SNODAS) snow water equivalent (SWE) maps and time series over the western U.S from your day of choice compared to average.
Example image of a NOHRSC National Snow Analyses map
Gridded snow data from the National Operational Hydrologic Remote Sensing Center (NOHRSC), also available in an interactive map.
Example image of a CA-NV River Forecast Center map
The CNRFC interactive website provides a full set of observations and forecasts, including snow data, observed and forecasted freezing levels, and streamflow forecasts.
Example image of a Colorado Basin River Forecast Center map
The CBRFC interactive website provides a full set of observations and forecasts, including snow and river conditions and water supply forecasts.
Western Water Supply Forecast Map
Website gives user access to all the western RFC water supply webpages.
Example image of a Northwest River Forecast Center map
The NWRFC interactive website provides a full set of observations and forecasts, including snow and river conditions and water supply forecasts.
Example of a Snow Cover Map
Daily maps, including animation tool, of northern hemisphere snow cover (white) and ice extent (yellow) from the U.S. National Ice Center. Click for current data.
Example image of a National Snow Probability Forecasts map
National Operational Hydrologic Remote Sensing Center (NOHRSC) snow probability forecasts depicting the probability of snowfall reaching or exceeding 4, 8, or 12 inches in the next 24 hours to 72 hours.
Example image of a CW3E West Coast Freezing Level Forecast map
The Center for Western Weather and Water Extremes (CW3E) uses GEFS forecasts to show probabilities for the western states’ watersheds of the freezing level being above or below the terrain height, i.e. forecast near-surface temperatures being above or below freezing, and precipitation falling as rain or snow.
Example image of a CW3E West-WRF Model
West Weather Research and Forecasting (West-WRF) is an ongoing effort at the Center for Western Weather and Water Extremes (CW3E) to develop a regional weather prediction system, including 3-hour and 24-hour snow, tailored to western U.S. weather and hydrological extremes.
Example image of a NRCS Streamflow Forecast Map
Available in spring and summer for the Western U.S., forecasts of percent of monthly average flow compared to data from 1981-2010.
Example image of a Sierra Nevada Water Storage Tracking map
Daily reservoir storage and snowpack update for the Sierra Nevada.
Example image of a California Data Exchange Center Snow map
Snow course and snow sensor information from California Department of Water Resources, including snow water content maps and time series by Northern, Central, and Southern Sierra. Click for actual conditions.
Real Time Spatial Estimates of SWE
Experimental research product provided by the CU-Boulder and NASA JPL that provides near-real-time estimates of snow-water equivalent (SWE) for the Sierra Nevada in California from mid-winter through the melt season.
Example image of a Airborne Snow Observatory map
NASA/JPL, in partnership with the California Department of Water Resources, has developed the ASO, an imaging spectrometer and scanning lidar system, to quantify SWE and snow albedo. Click for actual conditions.
Colorado’s Decision Support Systems SNODAS Tools
Colorado’s Decision Support Systems SNODAS Tools process the national SNODAS gridded dataset daily to provide data products, including Snow Water Equivalent and Snow Coverage statistics for Colorado water supply basins.
Example image of a CA-NV Snow Water Equivalent map
Monitoring from the UCLA Drought Monitor of current observed snow water equivalent (SWE) percent of average for nearly all California Department of Water Resources snow pillow stations.
Example of a PNW SWE map
Monitoring from the University of Washington Drought Monitoring System of current observed snow water equivalent (SWE) percent of average for nearly all NRCS SNOTEL stations, California DWR snow pillow stations, and a selection of British Columbia government snow pillow stations.
NRCS Water Supply Outlook Reports
Water supply outlooks produced monthly from January to May.
Example image of a CVTEMP map
NOAA Southwest Fisheries Science Center tool for modeled and observed temperature and flow data for the Sacramento River associated with Shasta Reservoir, Shasta Dam Operations, and meteorological conditions.
US Water Watcher Example Map
The US Water Watcher tracks water conditions from exceptionally wet to exceptionally dry using a number of different metrics including snow.
Example of NW Climate Toolbox Map
Snow Water Equivalent Percentile (1981-2010) based on VIC-gridMET data available through the Northwest Climate Toolbox HydroClimate Mapper at monthly intervals on the first of the month.
Intermountain West Climate Dashboard
Providing situational awareness of climate, drought, and water resources for the Intermountain West Drought Early Warning System including briefings.