Showtime. Temperatures Are Surging to Unparalleled Highs.

What is going to happen during the next few hours can only be described as weather whiplash.

Here is the latest super high-resolution temperature forecast for 5 PM today over western Washington.  Much of the western lowlands away from the water will be above 104F (light brown) and limited areas will surge about 110F.  I expect some localized hot spots around 115F.  Just extraordinary.   You will also note the onshore movement of cool air off the coast: an incipient onshore push of marine air.


SeaTac Airport is now running 8 degrees above normal and with its record-breaking 104F yesterday, it will certainly get near 110F today. Particularly since it is in a particularly favorable area of easterly downslope flow off the Cascades.

The difference between the temperatures at 11:30 AM today and yesterday is quite revealing (see below). MUCH cooler along the southwest coast (15-35F!), but much warmer from Seattle southeastward.  This is the result of the well-predicted southeasterly flow descending the Cascade slopes.



The current visible satellite imagery shows the cloud-laden cool area moving northward up the coast.  Our future comfort depends on it.


The cool-down tonight over Puget Sound still looks good: here are the latest high-resolution ensemble (many forecasts) predictions for SeaTac.  High of 110F this afternoon, but lows below 70F tonight.  Tomorrow will ONLY be in the upper 80s.  And back to normal on Wednesday.


Did you notice the hazy skies?  (see below)  No real wildfires in the region, so it isn't that.



I asked a local air quality expert, Phil Swartzendruber of the Puget Sound Clean Air Agency.   He suggested it is "secondary photochemical formation."   Translation: photochemical SMOG.  

The kind of unpleasant conditions that Los Angeles was so well known for.  The reason for this unpleasant bounty:  lots of sun and very warm temperatures that promote photochemical reactions (interactions of ultraviolet light with organic volatiles and nitrogen oxides).  As shown below, air quality has declined to moderate (yellow colors) around the region.



Finally, where do you think the warm air over us came from?   Well, I was curious and ran some air parcel trajectories back in time (such trajectories show the three-dimensional paths of air parcels reaching a point).  I went back 48 hours.

For this exercise, I traced back the air over SeaTac Airport at 100 meters, 500 meters, and 1000 meters above the surface (see below).  The top panel shows their position and the bottom panel provides their elevation.  

Wow...the air started well above the surface (roughly 3500 to 5000 meters) and then rapidly descended during the last day as it swung around the major high-pressure area over the region.   The air started warmer than normal aloft and warmed rapidly as it descended.


Stay cool.   Marine air is on the way for the west.  But then attention turns east of the Cascades.  Will the all-time high temperature for Washington State be broken (118F)?

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