When Does It Snow In Washington State

March 19, 2024

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How much Washington’s snow accumulates during the annual snow season has implications throughout the year. The snowpack is considered a crucial climate-related variable in the Pacific Northwest that affects water supplies for agriculture, fish, hydropower production and recreation.

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Washington’s rivers, lakes and reservoirs rely on mountain snow to supply water through the summer. Agriculture and outdoor recreation industries also depend on the snowpack for irrigation and water to support salmon and other fish habitats. The annual snow season typically lasts from October to May.

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We’re tracking this season’s snowpack through maps and charts to better understand our water supply in 2024.

CURRENT SNOW SEASON

The 2023-24 snow season had a slow start in the Lower Yakima and the Upper and Lower Columbia basins, which were mostly gone by mid-November. The end of November saw the majority of Washington’s basin below 50% of the 1991-2020 median. Last season saw the end of November with most of the state’s basins well over 100% of the 1991-2020 median, except for the Olympic and Central Columbia basins.

The first 10 days of December saw a series of atmospheric rivers flow into Washington and western Oregon, bringing record-breaking rainfall and above-freezing temperatures which further reduced what little snowpack there was.

Continuing rain from the Pacific along with above-freezing temperatures at the higher elevations saw Dec. 23 with only the Upper Yakima basin at 74% of the 1991-2020 median. Most of Washington’s basins were between 50% and 67%. The Olympic basin was at 28% and the Lower Yakima basin was at 35%. Last season, December ended with most of the state’s basins at or over 110% of the 1991-2020 median. Only the Olympic and North Puget Sound basins were below 100%.

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January 2024 has started out with all the state’s basins below 70% of the 1991-2020 median. Most were below 65% until a couple of system from the North Pacific began to move across Washington, bringing colder temperatures and precipitation, in some areas freezing rain, to lower elevations and snow to the passes which brought much of the Western Cascade basins and a couple of the eastern basins to over 80% including the Upper Yakama (86%) and the Lower Snake (83%). Toward the end of January, a series of warm South Pacific atmospheric rivers hit the western Pacific Northwest, bring warmer temperatures and rain. As of Jan. 31, the majority of Washington state’s basins are under 80% of the 1991-2020 median — Lower Columbia (75%) is the highest of the Western Cascade basins. The Olympic basin (33%) is the lowest in the state. The eastern Cascade basins are also dropping — The Upper Yakima (82%) is the only basin over 80% of the 1991-2020 media in Washington. The Lower Yakima and Spokane basins are at 57%. The Lower Snake (79%) has dropped below 80%.

The end of January last year saw most of Washington’s basins at or above 90%, with the Upper Columbia basin the highest (113%) followed by the Lower Columbia basin (104%) and the Lower Snake (101%). North Puget Sound basin was the lowest (79%) followed the Olympic basin (82%).

February 2024 started with above freezing temperatures and rain for most of the state. Oregon and Washington received the very weak end flow of an atmospheric river system that hit Southern California, soaking the Los Angeles and San Diego areas with heavy precipitation. From Feb. 14 through Feb. 19, a cold front moved through from the south which brought snow to Northern Oregon and Washington’s southern basins, but winds from out of the northeast kept the northern basins from receiving any. The end of February saw the West Coast get hit by a large system from out of the North Pacific with cold air, rain and mountain snow falling on Western and Southern Washington basins. As of Feb. 29, Washington’s basins were below 85% of the 1991-2020 media. The Lower Snake basin (84%) was the highest followed by Upper Yakima (83%) and Lower Columbia (79%). The Olympic basin was raised from 34% to 43%, still the lowest followed by the Lower Yakima basin (56%).

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Feb. 28, 2023 saw the state’s basins at or above 84% of the 1991-2020 media with the Lower Columbia basin (108%) was the highest followed by the Upper Columbia basin (106%) and Central Puget Sound basin (103%). The Lower Yakima basin (84%) was the lowest followed by the Olympic and North Puget Sound basins at 89%.

A massive front hit the West Coast over March 2 to March 4 and dropped large amounts of snow along the Sierra Mountains between California and Nevada, also brought cold air and snow to Oregon and Washington. All of Washington’s basin saw a much need increase. Lower Snake basin (90%) was the highest followed by the Lower Columbia basin (86%) and the Upper Yakima (82%). The Spokane, Central Columbia and South Puget Sound basins increased to 71% of the 1991-2020 media. The Olympic basin increased to 51%.

The start of March 2023 saw most of Washington basin’s above 90% of the 1991-2020 media. The Olympic basin was at 94%. The highest was the Lower Columbia (110%) followed by Central Puget Sound (106%) and Upper Columbia (105%). The lowest was the Lower Yakima (83%) followed by North Puget Sound (88%) and Central Columbia at (89%).

MARCH SNOWPACK