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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.

February Snow Drought Update

Types of Snow Drought

There are two types of snow drought based on the AMS Glossary of Meteorology:

A ruler buried in snow
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

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.&nbsp;
Value Map Hex Color
No basin value #767676
SWE Percent of 2004–2021 Average
Range Map Hex Color Description
0% - 0.01% #ffffff Trace or No Snow Current snow water equivalent (SWE) is less than 0.01% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
0.01% - 5% #543005 0.01%–5% of Average SWE Current snow water equivalent (SWE) is between 0.01%–5% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
5% - 25% #8c510a 5%–25% of Average SWE Current snow water equivalent (SWE) is between 5%–25% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
25% - 50% #bf812d 25%–50% of Average SWE Current snow water equivalent (SWE) is between 25%–50% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
50% - 70% #dfc27d 50%–70% of Average SWE Current snow water equivalent (SWE) is between 50%–70% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
70% - 90% #f6e8c3 70%–90% of Average SWE Current snow water equivalent (SWE) is between 70%–90% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
Range Map Hex Color Description
90% - 110% #8a8a8a 90%–110% of Average SWE Current snow water equivalent (SWE) is between 90%–110% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
110% - 130% #c7eae5 110%–130% of Average SWE Current snow water equivalent (SWE) is between 110%–130% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
130% - 150% #80cdc1 130%–150% of Average SWE Current snow water equivalent (SWE) is between 130%–150% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
150% - 200% #35978f 150%–200% of Average SWE Current snow water equivalent (SWE) is between 150%–200% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
200% - 400% #01665e 200%–400% of Average SWE Current snow water equivalent (SWE) is between 200%–400% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.
400% - 800% #003c30 400%–800% of Average SWE Current snow water equivalent (SWE) is between 400%–800% of the average SWE value for this two-day period, compared to historical conditions from 2004–2021.

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.

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.

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%.

The Rocky Mountains covered in snow and trees

Snow Drought Research and Resources