Saturday Weather Trifecta: Strong Winds, Major Mountain Snow, and Heavy Rain

FastCast—Friday, Dec. 10 to Saturday, Dec. 11:

Active weather is ahead for Western Washington, starting Friday afternoon. Three main impacts are expected…strong winds, significant mountain snow, and heavy rain. Winds will begin Friday evening, peaking early Saturday morning with gusts of 40-55 mph in the interior lowlands and 50-60 mph on the coast and in the North Sound. Power outages and tree damage is possible…and be sure to secure any holiday decorations! Mountain snow will be significant. Major totals of 24-36 inches are expected at the passes from Friday to late Saturday. This snow will be impactful, and travel across the mountains will be difficult, especially on Saturday. Rain in the lowlands will be heavy at times from late Friday night to Saturday evening, totaling 0.75-2 inches around Western Washington. Continue reading the blog below for more information on the three main impacts.

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Active weather is upcoming for Western Washington, mainly from Friday evening to late Saturday. The blog below will take a look at the 3 main weather impacts: winds, mountain snow, and rain.

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Winds:

As the system (and associated front) moves in late Friday night to Saturday, a strong pressure gradient will develop due to low pressure over interior BC. In the UW model below for 1 AM Saturday, you can see the tight gradient (close black lines over the PNW & offshore waters).

This gradient will fuel strong south winds, increasing Friday night, peaking early Saturday morning, remaining breezy through Saturday evening. Gusts of 40-55 mph are expected in the Interior Lowlands, prompting a Wind Advisory (below) from 7 PM Friday to 10 AM Saturday.

A High Wind Watch is in effect for the coast, Admiralty Inlet, and areas from Skagit County northward. Gusts of 50-60 mph are expected in those areas.  

Power outages and tree damage is possible, especially due to the high amounts of rain over the past few weeks. 

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Mountain Snow:

The most significant mountain snow of the season so far is expected from Friday evening to Saturday night. The NWS Seattle graphic for snow from Friday night to Saturday night is below.

Major totals of 24-36 inches are expected from the Paradise area northward and the Olympics, including Snoqualmie, Stevens, and White Passes. Incredible totals of 48-60 inches and 72+ inches are expected at Mount Baker and Paradise!

Precipitation will likely begin as rain/snow mix or potentially freezing rain at Snoqualmie Pass on Friday morning, becoming all snow by midday. (Stay tuned for an update on this tomorrow).

Expect very wintry driving conditions. Considering that I-90 eastbound has closed 4 separate times on Wednesday and Thursday (with less snow than the upcoming storm), there will likely be some travel delays across the mountains, especially on Saturday. 

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Rain:

Since this system will be associated with a strong cold front, lots of rain (heavy at times) is expected from Friday evening through Saturday morning, becoming showery through the day on Saturday. Below is the high resolution HRRR forecast for rain through Saturday afternoon. (Rain amounts shown for the mountains will be snow).

Expect the most rain from Friday evening to Saturday morning, totaling 0.75-1.25 inches in the lowlands, and 1-2 inches on the coast. There will also be a decent Olympic rain shadow, so areas around Port Angeles and Whidbey Island will only get up to 0.25” of rain. 

Importantly, river flooding is not expected to occur except on the frequently flooded Skokomish River in Mason County. This lack of river flooding is due to snow levels never rising above ~3,400 feet during this system.

A lot of weather is ahead…stay tuned for an update by late Friday evening!