SEATTLE, Wash. — Ending late tonight for areas near Cascades (wind diminishing after 2 am) Christmas Day and Thursday (for increasing lowland rain and wind and heavy pass snow)
A very active weather pattern is ahead for this week throughout Western Washington with multiple impacts varying by location.
A potent low-pressure system (that qualifies for bombogenesis or “bomb cyclone”) is about 400 miles off our coast, heading north toward Haida Gwaii. Given the distance from this storm, it has just brought some advisory-level wind gusts (45-50mph) to a few isolated spots like North Bend this evening. Given the label “bomb cyclone”, bombogenesis only pertains to the rate of intensification of a low-pressure center (24 millibar pressure drop in 24 hours), and does not have anything to do with storm impacts.
The system will diminish as it moves into British Columbia by daybreak, and winds will be falling off after about 2 a.m.
It will also be rainy tonight into tomorrow morning but the rain will be quickly tapering by daybreak and a few scattered showers and sunbreaks can be expected through the balance of Tuesday. Highs will be in the upper 40s to low 50s. In the mountains, a mixed bag of sleet, freezing rain, rain, and snow is expected overnight. Travelers should check conditions before heading across the passes into Tuesday morning, though conditions should improve as the day goes on.
At the beaches, high surf and crashing waves will pose a danger tonight through Tuesday morning.
A relative lull in the wet and windy weather will last from Tuesday into Christmas morning but another weather system evolve swinging a front into the area in the late morning through afternoon hours on Christmas Day. This will bring plenty of rain into the coast, the lowlands, and increasing snow in the Cascade passes. A Winter Storm Watch has been issued for the Olympics and Cascades starting Wednesday afternoon.
The rain and mountain snow will continue through Wednesday night and into Thursday morning, but some forecast models depict a small area of low pressure developing and impacting the region late Wednesday night and Thursday morning, with increasing winds in the lowlands and the coast. We could see some 35-45mph gusts in lowland areas Christmas night into the day on Thursday if this indeed pans out, with stronger gusts possible at the beaches and north. We’ll be monitoring the wind potential.
As for the mountain snow, expect 18-24 inches of new snow above 3,500 feet elevation from Wednesday afternoon through Thursday. This includes Stevens Pass, White Pass, Mount Baker, Paradise, and Hurricane Ridge. At Snoqualmie Pass, expect lesser amounts of snow on I-90, but we could still see 6-12 inch accumulation with periods of freezing rain. Regardless, this is a significant impact to cross-mountain travel for late Christmas Day and Thursday. Travelers are urged to check travel conditions before heading out and make sure vehicles are winterized and have chains and emergency supplies.
While this weather system fades late Thursday, more rounds of wet weather will impact the region Friday through the weekend, and it is likely to get windy once again, though details are murky with such fast-moving complex weather systems. It is apparent that with rounds of heavy rain, the risk of shallow landslides will continue to increase through the weekend and into next week. Mountain snow will also be a hindrance to travelers just about each day through the weekend.
We could turn cooler and drier for a time early next week.
As of 10 p.m. on Tuesday night, around 10,000 people were without power in Western Washington. Almost 8,000 Puget Sound Energy customers were without power, with many in the Sammamish area after high winds took down trees and powerlines.