After a few days of chilly and slightly unsettled conditions, stormy weather has once again returned to the Pacific Northwest. And with our latest system, the big story is snow in the mountains.
Winter storm warnings are in effect for the Olympics and Cascades, with storm totals of 1-2 feet over the Olympics and 2-4 feet among Western Slopes of the Cascades by Wednesday morning expected. The Eastern Slopes of the Cascades will see slightly less; 1-2 feet along peaks, and 5-12 inches in the valleys, but this is still a ton of snow for them as well. The snow level is expected to remain near 2,000 feet throughout the period, meaning all travel across the passes will be impacted.
Take a look at I-90 right now from Denny Creek to Cle Elum. Denny Creek is only at 1,800′, but the road is completely covered with snow.
Over Snoqualmie, chains are required on all vehicles except all-wheel drive, while chains are required for vehicles over 10,000 pounds crossing Stevens and White Passes. Stevens Pass will close from 3-6 AM for avalanche control, and I would expect the others to follow suit later today. There is currently “High” avalanche danger in both the Cascades and Olympics, so it is wise to avoid backcountry travel at this time.
The reason for this heavy snow is due to a strong cold front passing through our region. Most of the snow that has fallen so far has been pre-frontal; i.e. it has fallen in the zone of precipitation ahead of the front. The front just recently passed through the Washington Cascades, and is approaching the Northern Oregon Cascades early this morning.
Credit: UW Atmospheric Sciences
Snow will continue to pile up in the mountains today and tonight due to showers behind the front (the post-frontal precipitation). Here in the Western Washington lowlands, these showers are generally scattered and spotty in nature, but the terrain of the Olympics and Cascades forces the cool, unstable, post-frontal air over our region upward, enhancing showers over the windward slopes of those mountains. As a result, snow will continue to steadily pile up in the mountains until Wednesday morning, when a weak ridge builds over the area and onshore flow decreases. Another system comes through Thursday, delivering another solid dose of snow to the mountains.
72-hour snowfall amounts from 4 pm Monday to 4 pm Thursday are extremely impressive on the latest ultra-high resolution UW WRF. There are even some whites in there… off the charts for snowfall amounts!
Credit: University of Washington Atmospheric Sciences
Many models have been consistent in transitioning to a much colder pattern to start off 2017, with the coldest temperatures so far this season and the potential for lowland snow. I’ll blog about this tomorrow.
Have a nice day!
Charlie
