No FastCast tonight, but continue reading below for an important update on the incoming arctic air and frigid temperatures.
After a significant storm on Monday and Tuesday, a major weather change is ahead for the Pacific Northwest, as arctic air moves south from Canada into the region. This arctic air intrusion will begin with a modified arctic front moving southward through Western Washington on Thursday. This modified arctic front will usher in very cold temperatures, brisk and very cold northerly winds, and a chance of brief snow along the frontal boundary.
We'll start with the European model forecast for temperatures around 1 PM Thursday.
At 1 PM, the European model shows temperatures in the mid 20s in Whatcom County, in the mid 30s from North Seattle to Mount Vernon, and in the low 40s from Seattle southward. In Eastern Washington, it is generally in the upper teens to low 30s north of I-90, while areas to the south are in the mid 30s to low 40s.
Next, the forecast for 7 PM Thursday.
By 7 PM, everywhere from Olympia northward is below freezing, with Skagit and Whatcom Counties in the mid teens to low 20s. In Eastern Washington, the arctic front is just north of the Tri-Cities, with areas north of the Tri-Cities having temperatures in the low teens to mid 20s, except in the single digits in the valleys of the North Cascades.
So, the modified arctic front will move from north to south through Washington between Thursday morning (areas near the Canadian border) and late Thursday evening (areas near the Oregon border).
Along the frontal boundary, there is a chance of localized snow bands and snow showers. Additionally, any snow that falls will likely stick to most surfaces, as temperatures will be cooling rapidly with the arctic front.
Let's take a look at the snow forecast through early Friday morning, starting with the European model. This forecast shows the highest possibility for snow along the I-5 corridor being from Thursday afternoon to early Friday morning.
The European model shows a dusting to 1" of snow for most of Western Washington with the arctic front, with isolated areas getting over 1". In Eastern Washington, it's a similar story, with 1-2" of snow due to the arctic front. The exception is areas along the Idaho border, where 2-4" of snow is possible. Expect 6-12" of snow at the passes through Friday morning, making for difficult travel conditions at times.
Next, let's take a look at the GFS forecast for Thursday's potential snow, seen below. This forecast shows the highest possibility for snow being from Thursday afternoon to very early Friday.
The GFS forecast shows a similar pattern of a dusting to 1" for most of Western Washington, with isolated higher totals, including along the Strait of Juan de Fuca, a typical spot that is enhanced by northerly winds. This forecast indicates up to 6" possible along the Strait. The GFS gives a dusting to 3" for most of Eastern Washington around the periphery of the Columbia Basin, plus 10-16" at the passes.
Finally, here is the high-resolution NAM model, showing total snow through early Friday, and generally agreeing on timing, starting snow across the state on Thursday afternoon.
The NAM forecast is more conservative for snow, showing only a trace to 0.5" from Bellingham northward, around Everett and Lake Stevens, and from Seattle southward. Eastern Washington receives very little snow at all in this scenario, while the passes will get 4-8".
As the arctic front moves south on Thursday, it is also going to be breezy, both strong and cold northerly winds out of the Fraser and Okanogan River Valleys and breezy southerly winds to the south of the arctic front, before its arrival. Once the front arrives, winds will shift from southerly to northerly. Below is the HRRR high-resolution forecast for peak winds across Washington.
Notice strong 40-45 mph Fraser outflow winds in Whatcom County and 40-50 mph outflow winds in the Okanogan River Valley. Additionally, winds will gust 35-40 mph on the coast, 40-50 mph between Walla Walla and the Central ID Panhandle, and 30-40 mph across most of Eastern Washington. Also, note 40-60 mph gusts in the Cascades, which could bring areas of blizzard conditions on Thursday.
Last (but definitely not least), let's take a look at forecasted morning low temperatures on Friday morning from the European model.
These temperatures are very rare for Washington. On Friday morning, expect lows from Everett south to be in the mid teens to low 20s, with areas from Everett northward dropping to the mid single digits to low teens. Eastern Washington will drop to -10° to +5°, except in the low to mid single digits in the lower Columbia Basin. Even the coast is expected to reach the mid teens to low 20s. Mountain towns will drop to -10° to 0°.
What will be even more hazardous to the population is the wind chill temperature. Below is the European model forecast for wind chills (the "feels like" temperature) around 10 AM Friday.
Fraser River outflow will bring very cold wind chills of -5° to -15° for Whatcom and San Juan Counties, with extremely dangerous wind chills of -5° to -30° for Eastern Washington. Wind chills below zero can bring frostbite in under 30 minutes. On Friday morning, expect wind chills across the remainder of the lowlands and on the coast to be in the 0° to 15° range.
Please take all necessary precautions to protect yourself, your pets, and your home from these extreme cold temperatures. Make sure to drip your faucets, bring in any sensitive plants, and use heat sources to keep warm inside. Cold snaps can be just as deadly as heat waves.
With extreme cold weather and potential snow expected over the next 4-5 days, I will be doing daily updates at least through this weekend, so stay tuned.
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