Data & Maps

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.

View WY23 Snow Drought Summary

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

A forest with some partially melted patches of snow

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.

Snow Water Equivalent (SWE) Conditions

SNOTEL SWE SNODAS SWE

This map shows snow water equivalent (SWE)—the amount of liquid water the snowpack contains—at Snow Telemetry (SNOTEL) stations across the western U.S. SWE is displayed as a percent of the 1991–2020 median values for each station. Only stations with at least 20 years of data are included in the station averages.

Yellow to red hues indicate below-normal SWE, while blue hues indicate above-normal SWE. This map is valid through the end of the day November 28, 2023, with data updated on November 29.

View an interactive version of this map.

Source(s):

USDA Natural Resources Conservation Service

This map shows SNODAS snow water equivalent (SWE, the amount of liquid water contained within snowpack) for the past two days, as a percent of the 2004–2021 average. 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.

Source(s):

NOAA

Percent of Median Snow Water Equivalent

50%

70%

90%

110%

130%

150%

Percent of Median Snow Water Equivalent
Range	Map Hex Color	Description
0% - 50%	#e80000	< 50% of Median Current snow water equivalent (SWE) is less than 50% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
50% - 70%	#e39a00	50%–70% of Median Current snow water equivalent (SWE) is between 50%–70% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
70% - 90%	#e6e500	70%–90% of Median Current snow water equivalent (SWE) is between 70%–90% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
90% - 110%	#4ee504	90%–110% of Median Current snow water equivalent (SWE) is between 90%–110% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
110% - 130%	#70ffdd	110%–130% of Median Current snow water equivalent (SWE) is between 110%–130% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
130% - 150%	#00a9e4	130%–150% of Median Current snow water equivalent (SWE) is between 130%–150% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.
150% -	#0100fe	>150% of Median Current snow water equivalent (SWE) is greater than 150% of the median SWE value for this day of the year, compared to historical conditions from 1991–2020.


Value	Map Hex Color
No basin value	#767676

SWE Percent of Average (%)

0.01

110

SWE Percent of Average (%)
Range	Map Hex Color
0 - 0.01	#ffffff
0.01 - 5	#543005
5 - 25	#8c510a
25 - 50	#bf812d
50 - 70	#dfc27d
70 - 90	#f6e8c3
90 - 110	#8a8a8a

110

130

150

200

400

800


Range	Map Hex Color
110 - 130	#c7eae5
130 - 150	#80cdc1
150 - 200	#35978f
200 - 400	#01665e
400 - 800	#003c30

Data Valid: 11/28/23

Data Valid: 11/29/23

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Learn more about these data

Data and Map Gallery

A collection of tools for accessing observed and forecasted snow data, including snow and river conditions, freezing levels, streamflow and water supply forecasts, ice cover, reservoir storage, and more.

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).

1980 - present

images

NOHRSC National Snowfall Accumulation Map

NOHRSC National Snow Analyses

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

2003 - Present

images

text (ascii)

Example graph showing Western Sierra reservoirs plus snowpack

Sierra Nevada and Upper Colorado River Basin Water Storage Tracker

The CNAP Sierra Nevada Water Storage Tracker provides daily reservoir storage and snowpack information.

Current Conditions

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Example time series of freezing level information

CW3E West Coast Freezing Level Forecasts

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

Current Conditions

other

Example map showing change in snow water equivalent for the Western U.S.

National Snow and Ice Data Center Snow Today

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.

Current Conditions

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other

Interactive map showing streamflow forecasts

Streamflow Forecast Maps for the Western United States

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.

Current Conditions

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View More Data & Maps

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.

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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.

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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%.

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