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.

The great disappearing low. Where will it go?

 The infrared satellite image tonight is impressive, with a beautiful convergence of clouds into the low center west of the Olympic Peninsula (see below).

But you have to feel sorry for this low:  it is collapsing as it approaches landfall.

All of the modeling systems agree on the collapse, but there are subtle differences model solutions.

And that will influence what happens to us.

 For example, the American GFS model at 4 PM today (Monday) showed a potent low center of 972 hPa central pressure:

But my 7 AM Tuesday it was a wimpy 1003 hPa.   Sad.

The NOAA HRRR model forecast for the same time (7AM) is about 1000 hPa and the low center is a bit further to the west:

While the UW WRF model has a 999 hPa low a little further to the east.

Finally, the uber-accurate European Center model drops the low to about 1000 hPa and takes it over Sequim.

You would think that such a disappearing low would not produce any winds of note over western Washington.  

But yet Seattle WindWatch, which presents a whole range of forecasts, is still going for decent winds over Seattle (see below, these are the strong winds ANYWHERE in the City, even close to the water).  Gusts to 30-40 mph are found in many models, with some going into the 40s.  

One thing that is helping maintain the winds is that there is relatively high pressure to the south so that even a poor excuse for a low can produce a large north-south pressure difference and strong winds.

But like the late-night commercial...there is more!   

As the low passes to the north, winds from the west will hit the Olympics and they descend on the NE side of the barrier.  As the air sinks, it warms by compression, which causes pressure to fall (warm air is less dense than cold air).  

As shown in the forecast map pressure map for  7 AM, the mini-low is predicted by the UW WRF model on the NE side of the Olymics, which contributes to a locally enhanced pressure gradient (change of pressure over distance) over western Seattle and the Kitsap area. 

A wind boost due to the terrain.

This kind of situation on steroids occurred in 1979 during the Hood Canal Storm, when a mini-low formed south of Port Townsend, resulting in winds reaching 100 mph (see below).  

Washington State residents had a very expensive bridge replacement after that.