Atmospheric River: Heavy Rain, Flooding, and Gusty Winds

 Stand For Freedom, Stand With Ukraine 🇺🇦 

FastCast—Sunday, Feb. 27 to Friday, Mar. 4:

An atmospheric river is moving in to Western Washington. Significant rain totals are expected, with 2-4 inches likely over the lowlands. The heaviest rain will fall from Sunday afternoon to early Tuesday morning. Urban flooding and standing water is expected. River flooding will also occur. Moderate to major flooding is expected on the Snoqualmie River basin and on the Cowlitz, upper Nisqually, Stillaguamish, and Skokomish Rivers. Gusty winds, up to 30-45 mph, are possible around the lowlands through Tuesday. Additionally, the atmospheric river will bring subtropical air. Highs will reach the mid to upper 50s on Monday and Tuesday, with lows in the mid to upper 40s.

—————————————————————

Continue reading the full blog below!

Update 9:20 AM Monday: Urban and Small Stream Flood Warning issued for the Puget Sound area from Everett southward, through 7 AM Tuesday. Alert below.

——————————————————————

After a relatively dry February, the month will end with a deluge. An atmospheric river will bring heavy rain and significant totals are expected by Tuesday. 

Below is the HRRR forecast for rain totals from Sunday morning to Tuesday morning.

Expect up to 4 inches in the lowlands. A significant rain shadow can be observed over Whidbey Island and the NE Olympic Peninsula. The coast and Coast Range will be hammered, with 4-10 inches of rain. 

This is all due to a potent atmospheric river aimed right at Western Washington. Below is the UW forecast showing the atmospheric river at 7 AM Monday.

This atmospheric river will impact the area from late Sunday to early Tuesday, peaking midday Monday.

Flooding is expected, both on rivers and in urban areas. The UW forecast below shows expected precipitation over the Puget Sound area from 4 AM Monday to 4 AM Tuesday. 

Dark purple, red, and orange colors indicate between 1.5 and 3 inches of rain in 24 hours (see the key on the right side of the graphic). This amount of rain, generally south of Seattle, will likely cause urban flooding. Be aware of ponding, small stream flooding, and flooding in low-lying areas. 

Also, notice the sharp cut-off in rain totals from North Seattle to the rain shadow. Port Townsend will get 0.1-0.2” in the same period that Tacoma will get 1.75-2”!

Widespread river flooding is expected as well. Below is the flooding forecast from the Advanced Hydrologic Prediction Service.

The most significant flooding will occur in the Snoqualmie/Snohomish/Tolt River system, where moderate to major flooding is expected. Snoqualmie Falls will be a spectacle on Tuesday! The Stillaguamish, upper Nisqually, and Cowlitz Rivers will also experience moderate to major flooding. In Eastern Washington, expect bankfull stage to minor flooding on the entirety of the Naches and Yakima Rivers.

Additionally, expect wind gusts of 25-40 mph in the lowlands at times between Sunday and Monday evening, and up to 50 mph on the coast. Avalanche danger will also be elevated due to high snow levels and heavy rain in the mountains.

Update 7 PM Sunday: Avalanche Warnings have been issued for the Cascades of Washington by the Northwest Avalanche Center (NWAC). 

Stay tuned for updates on the flooding on Twitter and from our local forecasters!