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Snow Drought

What is 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)

Current situation and impacts in the West

June 7, 2018:
Most snow-monitoring sites have already melted out in Oregon, California, southern Idaho, Utah, Colorado, and northern New Mexico, and the remaining higher-elevation snowpack in these areas is well below normal, with many sites at less than 25% of normal. A sharp contrast is found in pockets of the northern Rockies where sites have well above normal snowpack though melting is underway rapidly due to well above normal temperatures throughout the month of May. In Alaska most sites have lost all snow cover and are not currently reporting with the exception of several sites in the southern coastal ranges to the south of Anchorage. Sites that are reporting in Alaska are well below normal. [Next update scheduled for June 21, 2018]

A map of the United States, focusing in on the Western US and a second map of Alaska, shows the percent of 1981-2010 median snow water equivalent (SWE) based on SNOTEL site data from the United States Department of Agriculture Natural Resources Conservation Service for June 3, 2018. The SWE percent of 1981-2010 median values is displayed using a range from <0 to >200%. Most of the California Sierra Nevada mountains are well below normal, generally ranging from <0% to 50%. The same is true for the southern Cascade Range and Blue Mountains in Oregon and similarly in the Washington Cascades with the exception of few stations reporting 150 to >200%. Many locations in the northern Rockies through Wyoming and Montana have above median SWE, ranging from 100 to >200%. Meanwhile the Colorado River Basin and the southern Rockies into the Four Corners region are below to well below median, ranging from <0% to 50%. Stations in central and eastern Nevada no longer have snow cover and are there for not reporting. A map focusing in on Alaska, showing stations in south and southeastern Alaska are still reporting snow below normal, <0 to 75%.

USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 median snow water equivalent (SWE) over the western U.S. (left/top) and Alaska (right/bottom) for June 3, 2018. Only stations with at least 20-years of data are shown. For an interactive version of this map, including percent of period of station record median SWE, please visitNRCS.

A map of the United States, focusing in on the Western US, shows the SNOw Data Assimilation System (SNODAS) percent of average (2004-2018) snow water equivalent (SWE) for June  2, 2018. The SWE percent of average is displayed using a ranging from 0 to 400%. Most of the California Sierra Nevada mountains are below average generally ranging from 5-200% of normal. The same is true for the southern Cascade Range and Blue Mountains in Oregon with above average (some areas >200%) in the Washington Cascades. The northern Rockies through Wyoming and Montana have above average SWE, in some places as high as 200%-400% of average. Meanwhile the Colorado River Basin and the southern Rockies are below average. The northern Bitterroot Range in Idaho is near average. Finally, much western Montana is still well above average.

SNOw Data Assimilation System (SNODAS) percent of average (2003-2018) snow water equivalent (SWE) for June 02, 2018. Percent of average SNODAS processed using Climate Engine. Please note the shorter historical period of this dataset compared to the station data above.

 


A graph displaying daily SNOTEL snow water equivalent (SWE) for the Upper Humboldt River in Nevada. On the x-axis is the water year from Oct 1, 2017 to Sept 30, 2018 and on the y-axis is daily SWE in inches. A black line shows the 2018 SWE values through June 3, 2018. A red line shows the 1981-2010 median. A blue line shows 2015, a brown line shows 2016, and a green line shows 2017. The region is currently at zero inches SWE.

SNOTEL basin-wide average SWE time series for the Klamath River Basin in Southern Oregon and Northern California. Black line is this year and red line is the 1981-2010 median. The regional SWE peaked in mid March, and is currently at only 11% of normal SWE for this date.

 

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.
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.
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.
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.
Example image of a NorWeST Stream Temperature map
Regional stream temperature database and modeled stream temperatures scenarios in a variety of user-friendly digital formats for streams and rivers across the Western United States.
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.
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.