Heavy mountain snowfalls, record cold, extreme winds and lowland snowflakes.
Winter conditions have returned to the Northwest.
Last night, heavy snow fell on the Cascades, flooding nearly two meters in Stevens Pass and about one meter in Snoqualmie. The chain is now required for both turns.
BILLIONSnowfall is particularly heavy in the central Cascades. Why?
Because a region of convergence, forced by the Olympics, has produced an enhanced range of precipitation, stretching across Puget Sound and into the Cascades, something illustrated by radar images around 4 a.m. this morning. (red arrow shows band)
Cold air in two stages
A cold front in the Pacific, combined with an upper trough, moved through yesterday, with cooler air and a northwesterly (from the northwest) current overhead. Therefore, snow abounds in the Cascades. This is phase one.
During the second phase, cold air entered central British Columbia and pushed southeast of the Rockies, as the upper northwest ridge strengthened and widened to the southwest. Thus, for tomorrow morning, a very cold situation has been established (see surface pressure map at 8 a.m. Monday, color is a temperature of about 2500 ft above the surface).
Extreme cold, extreme cold air will be in BC and northeast Washington and eastern Montana, with modified arctic air over eastern Washington and northwest Washington. With high pressure over BC and a low center over southwest WA, cold air will push through the Fraser River Valley into Whatcom County and western WA.
The winds pushing into Bellingham and the San Juans will be very cold and intense, possibly reaching 40-60 knots (see 10 a.m. gusts forecast Monday). The dark blue is the strongest. Dangerous content for unprotected people.
With cold air moving in, temperatures will drop sharply across the Northwest, with temperatures peaking Tuesday and Wednesday morning. Lows in the 20s are low in the west (and some locations in the teens) and around 10 degrees Fahrenheit in eastern Washington, with colder locations reaching single digits.
Check out the National Model Minimum Temperature Predictions for Wednesday morning (picture below provided by WeatherBell).
Unusually low temperatures (near 0F) will be observed in eastern Oregon, and even the Willamette Valley will have some locations for the upper teens to drop.
Some places in our area will have record low daily temperatures (lowest temperatures on those days).
With such cold temperatures, you should protect vulnerable plants. The city government should ensure that the large number of homeless people in the area do not take to the streets. Strong winds will create dangerous cold winds in much of the area. Unprotected people can die from exposure.
Snow in the lowlands
I don’t want to exaggerate this. West Washington won’t see a major snowstorm. But some lowland residents will see patches of white, especially on Monday morning.
The “problem” is that the main upper trench will be south of Washington by the time primo cold air hits Monday. So strong snow pressure on the upper level will not be there.
Therefore, snow will depend on localized areas of upward vertical motion. Let me prove it.
The UW model snowfall forecast until 4pm today (Sunday) shows snow in the mountains due to cool currents in the northwest. Where the snow belongs.
But as cold winds sweep out of the Fraser River Valley and northwest Washington, they will be pushed upward by the Games and the predicted result will be heavy snow extending from the northeast of the Olympic Peninsula back to Whidbey Island. Normal rain color is the opposite.
Some snow is predicted to fall over Puget Sound (very light) at the leading edge of the arctic airstream pushing out of the Fraser River Valley.
In such a local, local boundary situation, the uncertainty is great. For example, here’s the latest forecast for the NOAA/National Weather Service’s HRRR model, which pushed a lot of runoff from the north into Puget Sound. The forecast is until 1 a.m. Sunday, but more snow is forecast on Puget Sound than in the UW simulation.
One way that meteorologists identify uncertainty is by using a composite of multiple forecasts. The University of Washington’s high-resolution population snowfall forecast for Seattle shows a wide variation in possible snowfall (see below), from 0.2 to 0.9 inches. There are no forecasts for heavy snowstorms. And the snow depth is always smaller than the snowfall.
Key point
The mountains are frozen with 1-2 meters of snow. Great for skiers and water sources. A little uncertain
It’s going to be very, even on record, Monday through Wednesday, with highs in western Washington just in the 30s and lowest in their 20s and teens. Eastern Washington and Oregon will be even colder.
Local snow will fall near sea level over limited areas west of Washington, with the northeast Olympics likely to be the highest, but there is a chance of light snow over Puget Sound as the “front North Pole” moving south.
Interesting
