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.