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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 snowmelt. 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

May 28, 2020

In the western United States, many observation stations are reporting snow water equivalent (SWE) of zero. Late May into June is climatologically when many mid-to-low elevation locations have completely melted out. At this time, long-term medians, or “normals”, of SWE is near zero. Low seasonal snowpacks and unseasonably warm temperatures in states like California, Nevada, Oregon, Washington, Arizona, and New Mexico have led to melt out occurring about one to three weeks earlier than normal. Other locations, like the Wasatch Range in Utah, saw above normal SWE on April 1 but have melted out already or are on the trajectory to melt out early due to extended warm and dry conditions. The poor late season snow conditions will lead to below normal mountain runoff this summer in these states as well as southern Colorado and parts of southwestern Idaho. The northern Rocky Mountains typically melt out a bit later due to higher elevation and colder climate. A near-to-above-average snowpack still remains in the northern Idaho panhandle and northwest Montana.

In Alaska, with the exception of parts of the southern Kenai range and one station in central Alaska, most locations have reached zero SWE. In the Fairbanks region of Alaska, above normal seasonal snowfall, particularly in March and April, led to melt out about one week later than climatology. In southcentral Alaska, the Kenai mountains melted out approximately a full month earlier than normal due to well below normal snowfall. For example, the Grandview SNOTEL (elevation 1100’) reached zero SWE on May 20. Its normal melt out date is June 18.

Typical drought impacts are likely in locations where the snowpack melted out early. These impacts include: reduced mid- and late-summer streamflows, increased stream temperatures, lower than normal soil moisture, early drying of vegetation and increased vegetation stress, and increased high elevation fire potential.

Two panels show USDA Natural Resources Conservation Service (NRCS) snow water equivalent (SWE) station values over the western U.S. (top) and Alaska (bottom) for May 25, 2020. Scales range from <0 (white) to >50 inches (blue). Filled dots show individual SNOTEL stations. In the top panel a map of the Western US shows nearly all stations near 0 inches except for primarily parts of the northern Rockies and Pacific Northwest. In the bottom panel the map of Alaska shows nearly all stations at 0 inches.

Two panels show USDA Natural Resources Conservation Service (NRCS) snow water equivalent (SWE) station values over the western U.S. (top) and Alaska (bottom) for May 25, 2020. Scales range from <0 (white) to >50 inches (blue). Filled dots show individual SNOTEL stations. In the top panel a map of the Western US shows nearly all stations near 0 inches except for primarily parts of the northern Rockies and Pacific Northwest. In the bottom panel the map of Alaska shows nearly all stations at 0 inches.

USDA Natural Resources Conservation Service (NRCS) snow water equivalent (SWE) station values over the western U.S. (top) and Alaska (bottom) for May 25, 2020. For an interactive version of this map please visit NRCS.

Panel shows USDA Natural Resources Conservation Service (NRCS) May-July forecast total volume for the 50% exceedance probability (median May-July total runoff) as a percent of 1981-2010 median over the western U.S. issued May 1, 2020. Scales range from <0% (red) to 100% (white) to >200% (blue). Filled dots show individual SNOTEL stations and filled polygons shows HUC-6 river basin averages from all stations within a given basin. In the top panel a map of the Western US shows below average forecast volume (orange to red) in CA, NV, UT, AZ, NM, CO, southern ID, and OR with near average or above (white to green) in WY, MT, northern ID, and WA.

USDA Natural Resources Conservation Service (NRCS) May-July forecast total volume for the 50% exceedance probability (median May-July total runoff), percent of 1981-2010 median, over the western U.S. issued May 1, 2020. Shaded polygons show percent of median for HUC-6 (hydrologic units) river basins. For an interactive version of this map please visit NRCS.
 

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.
Sample SWE Map for the Intermountain West
Experimental research product provided by the CU-Boulder and NASA JPL that provides near-real-time estimates of snow-water equivalent (SWE) for the Intermountain West 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.