FastCast—Friday, Dec. 10 to Saturday, Dec. 11:
An active Friday night and Saturday are ahead for Western Washington. Rain is moving in and winds are increasing as of Friday evening. Overnight, 0.5-1.25 inches of rain will fall, heavy at times. Winds will gust 40-50 mph in the interior lowlands and 50-65 mph in the North Sound and on the coast, with winds peaking from 10 PM to 7 AM. Power outages and tree damage is possible, especially due to the saturated soils. Mountain snow will begin overnight as well, mainly above 3,500 feet. At Snoqualmie Pass, expect a rain/snow mix, brief freezing rain, or rain before changing to snow by midday. Total snow accumulations of 1-3 feet are expected by Sunday evening, except up to 4 feet above 6,000 feet. Difficult mountain pass travel is expected, especially on Saturday. Continue reading the full blog below for more detailed updates.
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Winds:
Expect winds to increase through the evening and into the night around the area. Peak winds will occur from approximately 10 PM Friday to 7 AM Saturday around the area. Below is the high-resolution HRRR forecast for 2 AM Saturday.
Winds will peak around 40-50 mph (locally higher, especially near water) in the Interior Lowlands. Peak gusts of 50-65 mph are expected in the North Sound and on the coast. Winds will diminish starting Saturday morning, but will remain gusty at times through the evening.
Power outages and tree damage are expected, especially on the coast and in the North Sound, where sustained winds may reach a very strong 35-45 mph! Be sure to secure outdoor objects, especially those inflatable Christmas decorations.
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Mountain Snow:
Major mountain snow is expected through Sunday. The NWS Seattle graphic below shows totals from Friday night to Sunday morning.
Expect significant totals of 12-30 inches at the passes and 30-48 inches above 6,000 feet.
The wild card with this mountain snow situation is Snoqualmie Pass, where rain is expected due to the “warm sector”, before changing to snow some time on Monday morning. There is a slight chance of brief freezing rain early Saturday morning, but that is generally unlikely and will be short-lived if it occurs. Total snow at Snoqualmie Pass may be higher than in the graphic above depending on when the changeover to all snow occurs.
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Rain:
Steady rain in the lowlands is expected to begin Friday night, continuing through frontal passage, which will occur around 5-8 AM Saturday and will contain the heaviest rain. Below is the HRRR forecast for rain from Friday evening to Saturday night.
Expect 0.7 to 1.25 inches of rain in the lowlands, and 1-2 inches on the coast. Less rain is expected on the NE side of the Olympics due to the rain shadow. Flooding is expected on the Skokomish River in Mason County and is possible on the Newaukum River near Chehalis.
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