The Patterns of Warmth

I have always been fascinated by the complex temperature patterns of the region, controlled by our substantial terrain and land-water contrasts.

The warming period over the next few days presents a great opportunity to view such temperature structures, so let's take advantage of this period by viewing the ultra-high-resolution forecasts run at the University of Washington.

Starting with the surface (2 meters above the ground) air temperatures for 5 PM today, you find the warmest temperatures in eastern Washington (away from the cooling of the Pacific) and in the lowest elevation of the Columbia Basin and river valleys.

Far cooler at higher elevations in the Cascades and Olympics and near the waters of the Pacific and Strait.   Northwest Washington (e.g., San Juans and Bellingham) is cooler than the South Sound,

The Willamette Valley (including Portland) is the warmest area west of the Cascades due to its isolation from the cool Pacific.  Why? The coastal mountains are an effective barrier, and the Willamette Valley doesn't have sea level conduits to the Pacific like the Puget Sound region.

On Thursday, high pressure will build overhead and temperatures will warm, particularly over the Willamette Valley and southwest Washington, with a cool zone remaining on the coast.  Portland will be toasty, but Seattle will only peak out around 80°F.

 

Note that eastern Washington is almost unchanged.

Friday will be different:  MUCH warmer, as a ridge of high pressure aloft builds over the  West Coast.  

Upper-Level (500 hPa pressure, ~18000 ft)Friday afternoon)

Here are the predicted temperatures.... wow.  Portland is warmer (upper 90s) than the Columbia Basin, and Puget Sound (away from the water) is in the 80s. Still some relief on the coast and Northwest Washington.

Why is western Washington warming?  

Because easterly, offshore-directed flow reduces the marine influence and provides some compressional heating on the western side of the Cascades as air from eastern Washington descends the slopes.

The nice thing about living here is that it is almost always possible to escape the heat: you can go up in elevation, head to the water, or check out northwest Washington.  A Washington State Ferry ride is usually a good, cool bet, with the warmest period often producing interesting mirages.