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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

January 9, 2020

The large scale spatial pattern of snow water equivalent (SWE) anomalies in the Lower 48 has not changed much since our last update in early December: the Pacific Northwest generally remains below normal with a gradient to above normal as you move southeast into the Four Corners. However, the magnitude of these anomalies has changed significantly due a series of storms bringing above normal precipitation (for the past three weeks) to the Washington Cascades and a drying trend to the Sierra Nevada and Intermountain West. The core of the worst snow drought conditions has now shifted from the Washington Cascades to the central and northern Oregon Cascades. For HUC-6 Basins the Willamette Basin in Oregon currently has the lowest snowpack at 37% of median SWE while Washington Basins has improved to 55-75% of median. As of January 6 there are now no stations reporting record low SWE and only four stations in the Pacific Northwest reporting 2nd lowest SWE on record with one in Oregon, two in Wasington, and one in Montana.

Despite large improvements in precipitation deficits in the Washington Cascades, SWE gains were limited at lower elevations due to warm temperatures and rain instead of snow for much of December. Alpine Meadows SNOTEL, on the west slope of the Washington Cascades at 3500’ elevation, recorded 34.1” of precipitation between December 9 and January with only 11.5” of SWE gains. The most recent storms over the past week have brought colder temperatures and more snow accumulation at lower elevations compared to mid-December storms.

The poleward shift in the storm track has led to a drying trend south of the Cascades. Major storms in the Sierra Nevada have been absent since mid-December and many locations have fallen to near-to-slightly below normal SWE for this time of year. Small SWE losses have even occurred at some locations in the past week. At the Central Sierra Snow Lab, near Donner Pass California, SWE has declined from 13” on December to 12” on January 7 with 87% of median SWE. Overall, the Sierra is still in good shape with the Walker River Basin being the only HUC-6 below normal at 90% of median SWE.

Snowpack in south-central Alaska remain below normal with Kenai Peninsula and Prince William Sound HUC-6 basins at 56% and 50% of median SWE, respectively. In southeast Alaska there is only one station with long enough records to computes normals: Long Lake currently sits at 91% of median SWE. The few stations in the interior of Alaska currently reporting data all indicate above normal snowpack.

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 January 5, 2020. Scales ranges from <0% (red) to 100% (white) to >200% (blue). In the top panel a map of the Western US show above normal SWE (green to blue) in UT, CO, AZ, NM and below normal SWE (orange to red) in ID, WA, and OR, western MT, and western WY. In the bottom panel the map of Alaska show below normal (red to orange) in south central Alaska and above normal (blue) in central Alaska.
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 January 5, 2020. Scales ranges from <0% (red) to 100% (white) to >200% (blue). In the top panel a map of the Western US show above normal SWE (green to blue) in UT, CO, AZ, NM and below normal SWE (orange to red) in ID, WA, and OR, western MT, and western WY. In the bottom panel the map of Alaska show below normal (red to orange) in south central Alaska and above normal (blue) in central Alaska.

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 January 5, 2020. Only stations with at least 20-years of data are included in the station averages. For an interactive version of this map please visit NRCS

Map shows USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 average precipitation over the western U.S. for the period December 16, 2019-January 5, 2020. Scales ranges from <0% (red) to 100% (white) to >200% (blue). Above normal precipitation is found (green to blue) in WA, northern ID, and AZ and below normal precipitation (orange to red) is found over the rest of the region.

USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 average precipitation over the western U.S. for the period December 16, 2019-January 5, 2020. Only stations with at least 20-years of data are included in the station averages. For an interactive version of this map please visit NRCS.
 

Map shows University of Idaho’s gridded meteorological data (gridMET) mean temperature difference from the 1981-2010 average for the period December 13, 2019-January 3, 2020. Scale ranges from <-3C (blue) to >+3C (red). Above normal temperatures (orange to red) is found in the Pacific Northwest and south into the Great Basin and northern CA. Below normal temperatures (light blue to dark blue) is found in the Four Corners region and southern CA.

University of Idaho’s gridded meteorological data (gridMET) mean temperature difference from the 1981-2010 average for the period December 13, 2019-January 3, 2020. For an interactive version of this map please visit Climate Engine.

 

 

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.