Atmospheric River Continues, Warm Temperatures on Wednesday, and the Next Round of Flooding

FastCast—Tuesday, Jan. 11 to Friday, Jan. 14:

Western Washington is being impacted by another atmospheric river, with heavy rain at times throughout the day on Tuesday, mainly from Seattle southward and on the coast and in the mountains. Rain will continue through Wednesday morning in the lowlands and through the afternoon on the coast. Expect additional totals of 0.4 to 1.4 inches between Seattle and Olympia, 0.3 to 1.25” north of Mount Vernon, 1-3 inches on the coast, and 3-6 inches in the mountains. River flooding is expected, with most rivers rising or reaching bankfull. Flooding will be worst on the Snoqualmie, Skokomish, and Tolt Rivers. Warm temperatures are expected overnight Tuesday (near 50) and on Wednesday, when highs in the mid to upper 50s are expected, with a slight chance of hitting 60 degrees. This is due to the subtropical component of this atmospheric river. Additionally, snow levels will be very high, around 7,000-8,000 feet, through Thursday. Temperatures drop back to highs in the low 50s and lows in the low to mid 40s by Thursday and Friday.

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The second atmospheric river in less than a week is impacting Western Washington, with 4-6 inches of rain in the Olympic mountains, 1-3” in the Cascades, 1-2.5” on the Coast, and quite a spread of totals in the Lowlands. The highest amounts have been 0.5-1.6 inches from Olympia to North Seattle. A well-defined rain shadow is present from Everett to Mount Vernon (and will continue), and totals are 0.3-0.9 inches in the Northwest Interior.

Below is the HRRR forecast for additional rain from 6 PM Tuesday to 12 PM Wednesday.

The HRRR, like other forecast models, has shown an area of higher precipitation totals between Seattle and Olympia. If you live in these areas, be prepared for 0.5-1.3 more inches of rain and a higher chance of urban flooding. 

Generally, expect 0.3-1 inch of rain north of Seattle, 1-3 inches on the coast, and 3-6 inches in the Olympics and Cascades.

Subtropical air from the atmospheric river will bring significantly warmer temperatures on Wednesday. Overnight lows on Tuesday will only drop to the upper 40s to low 50s, then temperatures will soar on Wednesday. The HRRR forecast for temperatures at 1 PM is below.

Highs in the mid to upper 50s are expected, with temperatures potentially in the low 60s in parts of the lowlands. These will be our highest temperatures since late November 2021. 

It will also be on the muggy side, with dewpoints in the low 50s and relative humidity of 80-90%. (HRRR dewpoint forecast at 1 PM Wednesday below)

Don’t be surprised if you step outside on Wednesday afternoon and it feels muggy.

Also starting on Wednesday will be the next round of river flooding. The Advanced Hydrologic Prediction Service river food forecast is below.

Expect most rivers draining the North/Central Cascades and the Olympics to rise and potentially reach bankfull levels. Major flooding is expected on the Snoqualmie River in the Carnation area, with moderate flooding on the Tolt River above Carnation and Skokomish River at Potlatch. Minor flooding is expected on the Snoqualmie, Snohomish, Stillaguamish, Nooksack, Bogachiel, and Chehalis Rivers.

Stay tuned to Twitter and Michael Snyder's Pacific Northwest Weather Watch YouTube channel for the latest updates!