Late Winter Heat Wave With a Twist

 It felt like spring today in western Oregon and Washington, with some temperatures soaring into the 60s.

The high-temperature map for today (Wednesday) reveals low 60s east of Puget Sound and along the Washington coast and UPPER 60s along the Oregon coast.   In contrast, eastern Washington and Oregon were much cooler, with temperatures stuck mainly in the low to mid-50s. Even some 30s on the eastern slopes of the Cascades.

A close-in view around Puget Sound shows the contrasts (below), with 65F in Carnation, near the western footfills of the Cascades, but ten degrees cooler over western Seattle.

For many locations, this was the warmest day so far this winter.

So why was the coast so warm? Why so warm over the eastern suburbs of Seattle?

One can get a hint by looking at the regional sea level pressure pattern this afternoon at 2 PM (see below).  Relatively high pressure inland and lower pressure along the coast.

The pressure pattern forces easterly winds (from the east), directed from high to low pressure.

Such easterly winds remove the cooling effects of the Pacific.

It also produces downslope flow on the western side of the Cascades and coastal mountains.  This downslope flow produces localized warming as the air is compressed as it moves from lower pressure aloft to higher pressure near the surface.  Warming just like in your bicycle pump.

You can see this downslope warming effect in the temperature forecasts of the UW WRF model for 10 AM this morning/ Reds areas are the warmest temperatures.

At this time, the warmest temperatures are on the western slopes of regional terrain due to the downsloping, sinking air.  You can also see cool air (blue colors) being pushed up the eastern slopes of the Cascades.

Tomorrow should remain relatively warm over Western Washington south of Everett and over all of western Oregon but somewhat cooler along the coast as the easterly winds weaken.

Similar conditions on Friday, followed by a slow cool-down over the weekend.  Dry at least through Saturday.

Time to get the garden cleaned up or to enjoy that long-neglected outdoor recreation.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters. I will talk about the extended spring forecast and new AI forecasting technology.