Thanksgiving Forecast: Another Atmospheric River to Impact the PNW

 FastCast—Thanksgiving Day to Sunday, Nov. 28:

As if we haven’t had enough rain this month, another atmospheric river will impact the Pacific Northwest from Thanksgiving Day to midday Friday. Expect 0.5-1 inch of rain in the lowlands from Thursday evening to midday Friday. On the coast and in Whatcom County, expect 1-2 inches. The atmospheric river will raise snow levels over 8,000 feet and high temperatures will rise to the low-mid 50s by Friday and Saturday. Rain will be heaviest from Thursday evening to early Friday morning. A second atmospheric river arrives on Saturday, continuing through Sunday. This one will likely bring another 0.5-1 inch of rain in the Interior Lowlands, and 1-3 inches on the coast and north of Mount Vernon. This will likely be followed by a third atmospheric river from Tuesday to Wednesday. This one is more uncertain…so stay tuned. Of particular concern is the fact that 4-8 inches of rain will likely fall in Whatcom County and BC’s Lower Mainland, an area that is still just beginning to recover from devastating flooding. Stay tuned for updates on the river flooding potential…which is not very high as of Wednesday night, but the threat of landslides will definitely increase. Happy (wet) Thanksgiving!

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This Thanksgiving will be served with a side of atmospheric river. The first of three atmospheric rivers will move into the Pacific Northwest on Thanksgiving, with the heaviest rain from Thursday evening to Friday morning. See the UW model forecast below that shows the IVT (integrated water vapor transport) at 4 PM Thursday.

This has become a typical forecast model image for the PNW as of late. Due to this atmospheric river, temperatures will rise into the 50s and snow levels will rise over 8,000 feet. 

Below is the UW rain forecast through 4 PM Friday.

Expect 0.5-1 inch from Olympia northward in the interior lowlands. More rain will fall on the coast & in the mountains (1.25-7.5”), and less will fall in the rain shadow (0.1-0.5”), including Seattle. 

1-2.5 inches will fall in Whatcom County and BC’s Lower Mainland. This area is just beginning to recover from devastating floods, and the series of atmospheric rivers won’t help. Urban flooding and landslides are possible, and rivers are expected to reach “action stage” (at or just over bankfull) and minor flood stage in Whatcom County. 

Gusty winds of 35-45 mph are possible north of Everett on Thanksgiving, with gusts up to 20-30 mph elsewhere.

As additional atmospheric rivers move in, Thanksgiving weekend travel will be impacted, with the biggest impacts on the weekend, as atmospheric river #2 brings heavy rain to the entire region.

Stay tuned!