3D Northwest Heat

 We are now in a short warm spell with temperatures getting into the mid 80s to lower 90s in western Washington.  Cooler weather (and some rain) will arrive next week.

 But for me, one of the most fascinating aspects of our warmth is how three-dimensional it is.  How spatially varying the heat can be.

Let me show you, by starting with yesterday's highs (below). Mid-80s around Seattle, 70s and low 80s over Northwest Washington, around 100F in the Willamette Valley, and upper 90s in the Columbia Basin.   An interesting feature is the near 100°F in the higher terrain between Olympia and the coast,.

In western Washington, the influence of the cool Pacific and inland waters results in cold air near the surface, but warmer temperatures right above.  This is particularly true when (like yesterday) there is easterly  (from the east) flow aloft moving warmer air from eastern Washington towards the west.

Yesterday (Friday) morning, this situation was so profound that there was an inversion (temperature increasing with height) above Seattle, something illustrated by the temperatures above SeaTac Airport at 8 AM (below).  Temperatures in the mid-60s near the surface, but 70s above 2200 ft.  

A profound inversion from 1000 to 2500 ft (more than 10 degrees).  I bet morning hikers noticed this warming with height!

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This morning at 7 AM, the inversion was even stronger  (see below), going from 67°F to 79°F above 1500 ft.

The inversion weakened during the day as solar heating warmed the surface.

A temperature inversion can act as an atmospheric lens for weather radar beams, causing  the radar beam to bend downward to the surface, which acts as a target.

This inversion bending of radar explains the huge number of false radar echoes off our coast right now (see below).  The radar beam hits the ocean surface and then is reflected back. 

Looks like a lot of rain out there...in reality there is nothing.

When we have inversion conditions, maps of temperature can get jarring, such as this morning at 7 AM in the Cascade foothills near North Bend.  Around 70°F on ridgetops but lower 50s and 40s in valleys.

According to the latest National Weather Service forecast, the warmth will continue over the weekend, with cooling by mid-week.  Possible rain next weekend.

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.

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