May 11, 2019

Batten Down the Hatches: Cool, Marine Air is Surging Into Western Washington

There are few things I enjoy more than a good onshore push of marine air after a warm period.

The leaves start to rustle, the wind chimes sound, a pleasant coolness is experienced.

And it is happening right now.

The onshore marine push actually began earlier today as low clouds spread over the coastal zone, and then slowly pushed inland this afternoon (see visible satellite image below at 5:40 PM).

The traditional way to forecast an onshore push is to monitor the difference in pressure between pressure on the coast (Hoquiam) and over Seattle.  When it got to 3.5 hPa (millibars)--with higher pressure on the coast-- a decent onshore push would occur.   When it gets to 4 hPa, then a strong one could be expected.

Checking today's readings, the difference in pressure got to 4.2 hPa--- thus, a strong push should be expected (look at HQM-SEA, time is in UTC, 21 is 2 PM, 23 is 4 PM).   The models concur.

Observations at 5 PM showed the push in action, with  southwesterly winds  at Shelton, SE of the Olympics,  gusting to 36 mph at that time.   Strong winds (gust to 37 mph) were also pushing into the Strait of Juan de Fuca.

The onshore push will bring in cool marine air and the low clouds that were looming offshore.  Expect to wake up to cloudy, cool conditions on Mother's Day if you are in western WA.  Furthermore, strong northwesterly winds will descend along the eastern slopes of the Cascades in places such as Ellensburg, Yakima and Wenatchee.  Lots of wind energy will be generated!

Clouds should burn back from the western WA interior late morning and Mom will have an opportunity for a pleasant walk with the family.   But temperatures will be cooler, roughly 10-15F less than on Saturday.

Big changes are ahead, something I will talk about it another blog.   Expect the second half of the month to be radically cooler and wetter than the first half.


  1. Max temp in NW Bellingham today: 73.7F at 2:40PM

  2. Cliff,

    What good news!

    It was great to have a warm, sunny day. But, I'm equally happy to have the weather turn cooler for a while longer.

  3. good news.
    thanks as always for your work.

  4. Max temp today in NW Bellingham 60.3F


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