Extreme Morning Heat Wave Hits the Puget Sound Region

Major, long-term, temperature records are being broken this morning, with amazingly high temperatures around Puget Sound.  Stunning records.

I knew something was up when I walked my dog this morning around 6:15 AM.... it felt amazingly warm.   Then I checked and was floored.

Temperatures at 6 AM were in the mid-60s from Seattle to Tacoma (see graphic, click to expand).  50s over north Seattle.  Normal lows this time of the year are around 38-39F.

Sea-Tac Airport was 63F at 6 AM, with an overnight minimum of 62F.    The previous minimum temperature temperature record for the date was 50F--but temperatures will fall today....so we will have to see if we beat it.

We are talking about a stunning record low temperature.  The plot of temperature at Seattle illustrates this (normal highs and low temps plotted with purple and cyan color lines).  The low this morning was roughly 10F higher than our normal high temperatures.

According to my colleagues at the National Weather Service, the 5 AM PDT temperature at Renton, Washington (at 66 F) was the 2nd warmest spot in the lower 48 states....just behind Palm Springs, California (69 F). 
So what is going on?   A very strong easterly wind event with powerful downslope winds.   In fact, there is windstorm going on right now in the Cascades foothills, particularly around Enumclaw.   And strong downslope winds cause powerful compressional heating of the air, like in your bicycle pump.  Thus, the extreme temperatures.

Here are the temperatures and winds around Puget Sound.  Look closely (click on image to expand) and you will see that the warmest places have easterly winds.

The pressure gradient across the Cascades is very large now (7.5 hPa across the mountains, higher to the east) and the winds above Sea-Tac Airport (see below) shows a deep layer of easterly flow...and easterly flow that is very strong at low levels. ( the figure shows temperatures in red and wind barbs, time is on the x-axis and height in pressure on the y-axis, 850 is roughly 5000 ft).

The turbulent easterly flow is mixing down to the surface, working against any nighttime cooling by the emission of infrared radiation to space.  The strong easterly winds have gusted to 52 mph in Enumclaw and 30-40 mph as far west as the Sound and as far north as Issaquah.

Why are there strong winds and warmth between Seattle and Tacoma?  Because of a "weakness" in the Cascades to the east....what meteorologists call "Stampede Gap"---- see the terrain map below.

The winds and high temperatures will fade today....but those of you living between Seattle and Tacoma are experiencing an unusual event today.

from Cliff Mass Weather and Climate Blog http://ift.tt/2tOdsiM