February 12, 2025

Lowland Snow (AGAIN), Powerful Easterly Winds on the Eastside, and Central Oregon Temperature Drops to -38F

 Lots of weather action occurring or will soon happen.

Amazing Low Temps

Last night, many Washington State locations enjoyed their coldest low temperatures of the year (see below).  Teens were reached over much of western Washington and below-zero temps were evident across eastern WA.  Some snowy WA valleys (e.g., Mazama) reached -15F.



But the real crazy lows were in valleys within the high plateau of eastern Oregon, where several locations dropped below -20F.


But if you want insane cold, the hamlet of Seneca, just north of Burns, dropped to -38 F.

Strong Easterly Winds

 I have received several worried emails from folks living on the Puget Sound eastside, worried about powerful easterly winds.   These folks went through hell last November with the "bomb cyclone" event and are not a little shell-shocked from the experience.

As shown by the forecast map of sea-level pressure (solid lines) and low-level temperature for Thursday morning (7AM), there will be a large pressure difference across the Cascade between cold, high-pressure over eastern WA and a modest low-pressure area moving up the coast.   This will cause strong easterly (from the east) winds over the Cascades and the western foothills.

Below are the maximum surface winds predicted through Thursday at 4 PM, with the greatest winds in the familiar wind corridor south of I-90 from roughly Issaquah to Enumclaw and stretching towards Renton.

30-60 kts in places, but NOTHING like November.

Snow

As the offshore low-pressure area approaches the Oregon coast, snow will push northward, first over NW Oregon and then into SW Washington.

Predicted total snowfall (NOT SNOWDEPTH) through 4 PM Friday is shown below.  Light snow over the lowlands, but it won't add up to much.  More over the south Cascades and Olympics.  

The sinking easterly flow west of the Cascades noted above will greatly reduce the precipitation and snow over the eastern side of Puget Sound.  The opposite near the Olympics.


Turning to Seattle SnowWatch (supported by the City of Seattle), you can see the light snowfall Thursday night and Friday morning.  Not the end of the world.😀😄.  But it might get slippery...so drive carefully.










February 11, 2025

Modified Arctic Air Spreads Across Western Washington

 Does your skin feel feel dry?    Cracks in your skin?     Feeling chilled?

There is a reason:  modified Arctic Air has spread over western Washington.  And yes, cold, dry air is over eastern Washington as well.


Temperatures this morning (6 AM) were the coldest so far this year for many Washington State locations.  Temperatures dropped into the twenties and teens over western Washington, while single digits and even below-zero temps were observed in eastern Washington.


In such situations, there are often great temperature contrasts in western Washington between locations near the relatively warm Puget Sound and locations away from the water.  For example, one location in West Seattle was 30F while temperatures dropped to 18F in Redmond.   A chilly morning in Microsoft land.


Why so cold?    Clear skies allowed the Earth to radiate infrared energy to space.  However, the most important contribution was the influx of modified Arctic air from northern Canada. 

 A little cold-air tutorial first (as a professor of atmospheric and climate science I can't help myself 😀)

This time of the year, very cold air from northern Canada moves southward into the interior of the continent.    Such air generally does not get into western Washington because of the "protection" of two mountain ranges, the Rockies and the Cascades.


As shown by the figure below, for the cold air to get into western Washington the easiest (and lowest elevation) route is through the Fraser River Valley, exiting north of Bellingham (blue arrow),   Cold air from the interior of BC can also move into eastern Washington through the Okanogan Valley (orange arrow). 

Once the cold air gets deep enough in eastern Washington, some can move over the Cascades, but that air is warmed by compression as it descends the western slopes of mountains (red arrow).



Last night (10 PM), there was very cold air at the surface west of the Rockies and in the interior of BC (white color), with modified (warmed) Arctic air invading eastern Washington (purple color).


The "invasion" of cold, dry air from the BC interior through the Fraser River Valley was very obvious at 2 PM yesterday (Monday), with strong northeasterly winds (red colors are gusts in mph) and very low dew points (blue colors).


At Bellingham,  the surge of strong northeasterly winds, with gusts to nearly 45 mph, was clearly evident yesterday as the Arctic air moved in (see below).  


By later in the day, the dew point--an excellent measure of the dryness of the air--- started to plummet from nearly 30 to under ten.   The mark of the Arctic!  The temperature dropped later.


So no need to travel to Inuvik or Yellowknife, you are breathing the air from those regions today.









Lowland Snow (AGAIN), Powerful Easterly Winds on the Eastside, and Central Oregon Temperature Drops to -38F

 Lots of weather action occurring or will soon happen. Amazing Low Temps Last night, many Washington State locations enjoyed their coldest l...