June 20, 2018

Marine Air is Surging In

After a period of substantially above normal temperatures, the Northwest's air conditioning is now set to high, as cool, marine air pushes into western Washington tonight.

Meteorologists carefully study the pressure difference between the coast (e.g. at Hoquiam) and Seattle to appraise the situation.  When that difference gets to about 3 hPa, a good push is pretty much guaranteed.  Here are the latest numbers:

Hoquiam minus Seattle is now 3.6 hPa.... a guaranteed marine push.

The latest (10 PM) surface observations show that cool air has pushed into the Strait of Juan de Fuca and has already moved inland south of the Olympics.   Only central Puget Sound is in the 70s....and that will change quickly during the next few hours.

The visible satellite image at 7 PM clearly showed low clouds moving inland from the coast, while thunderstorms were evident over the Cascades (see below).

The cause of this marine push?   The movement of the high pressure ridge inland and the approach of an upper level trough (see upper level-- 500 hPa- map at 5 PM today).

Low clouds should be over most of western Washington on Thursday morning, with high temperatures only reaching the mid-70s.   Perfection.    And Friday will be even cooler, with highs only getting to the upper 60s, followed by a modest warming over the weekend.

The cooler air will be welcome.....my little dog has not liked the warm weather, preferring to sleep on the floor rather than in her normal chair.

Thursday morning addition

An interesting aspect of this marine push is how shallow it is.  Here is the time height cross section of temperatures (red lines) and winds above Sea Tac Airport (time is on x-axis and height (in pressure) on the y).  The cooling started around 06 UTC (11 AM PDT) and was pretty much limited to below 850 hPa (about 5000 ft).   So big cooling near sea level, but you would not notice it at higher elevations.

 The visible satellite imagery this morning shows nearly all of western WA covered in low clouds:


  1. it is unfortunate that the air conditioning is set on HIGH eight months out of the year

  2. Yes, it's unfortunate the climate here is like it is. Cliff, why do we have to have all this cool marine air around here? I never had to put up with this back home in southern California.

  3. Bite your tongue, Rod.

    It is that air conditioning that makes this place so appealing.

  4. But I think these "marine pushes" are boring. They don't come with ENERGY like a continental style front! No rain, no thunder and no lightning. I think Cliff said that they are generally too shallow to produce atmospheric instability; instead they usually only cool the surface, (if I remember right) actually increasing stability. If we can't water the garden let's have the sun back for the weekend.

  5. Cliff,
    On a different subject, very heavy fog today off the west side of Whidbey Island. As of 13:30 strong fog shows on satellite from about Port Townsend north to Cypress island and into Guemes Channel. What is causing so much fog today?


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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