November 21, 2018

Thanksgiving Forecast

A band of moderate rain is now moving through western Washington, but the good news is that it will clear the region by 3 AM Thursday.

There will be a period of dry conditions from roughly 4 AM to 1 PM around Puget Sound, so if you want to get your Thanksgiving walk or run in, this will be the time.

The 3-h precipitation totals ending at 7 AM shows dry conditions over the western lowlands (and a few showers over the mountains).   A juicy band of precipitation is offshore.

 The next three hour totals (ending 10 AM), show the frontal band making landfall.

And the 3-h rainfall ending 1 PM shows the wet stuff over Portland and just reaching Seattle.

The following several days will be characterized by lots of showers.  The 72h total ending 4 PM Saturday has up to 2-5 inches over WA terrain and 5-10 inches over some portions of northern CA.

But what really has me excited is the snow.  We will have cool, showery weather, with a low snow level. Over the next 72 h, 1-2 feet will fall above 4000 ft.  Cross country skiing will be possible by Sunday.

The precipitation totals over northern California so far in this storm have been moderate, with around 1.25 inches in the mountains behind Paradise, CA and a few locations getting 2-3 inches.  A lot more is coming.

The good news is that the California-Nevada River Forecast Center indicates little chance of flooding over California (since the ground is starting out so dry) and air quality has rapidly and profoundly improved over much of the Golden State.    To show this, here are the latest Air Quality Index values:  many are green, indicating healthful air.

So enjoy the return to normal weather and wonderful sound of rain on the roof and trees.


  1. That was the wettest Thanksgiving I've seen for years, and I've been in the NW for 70 years. There have been heavier Thanksgiving rains, but this was still notable. Rain intensity here in Wedgwood, NE Seattle was very heavy. We drove to my extended family in Issaquah and visibility on I5, 520, 405 and 90 was very limited. The rain continued until mid-evening. When we headed home by 8:00 PM it was down to light showers, then cleared on the way home, sufficiently so that we could see the moon. But rain returned later and has been on and off until now, Friday morning. I haven't checked our rain gauge yet but I'm betting it will be +1 inch, conservatively.

  2. Dr Mass: Ooh! This forecast has been spot-on, really accurate. I don't know if you run an eye over the reported measurements shown on CoCoRaHS' 24 hr maps*, but the pattern has been playing out as predicted day by day. Those worried about this new rain-year, so far (at least here in the north headwaters) since Oct 1 this year very closely resembles last year's precipitation. As for the model doing its stuff, the freezing level has dropped on cue to the predicted level(s). As NW weather watching goes, in blog parlance: "MEH" But as modeling goes - wow, thumbs up.


  3. Okay, I was wrong. We had a scant 0.95 of an inch in the gauge, proving once again that amateurs shouldn't try weather at home! But it did rain hard!

  4. This was the kind of storm where the Sequim rainshadow was in fine form. 0.06" on Thursday and 0.07" so far today at my house. We had bright sun for an hour or so this morning.

    When the weather is coming from the SSW to SW to WSW, the Olympics wring it all out, leaving us in the descending, warmer airflow coming down from the mountains. Which ensures the taps shut down until the rain clouds pass over us.

    We do get some rain when the weather comes from directly W to NW to NE. Due Westerlies coming down the strait aren't rare, but moisture from NW to NE is rare.

    We only get clobbered when strong Fraser River Outflows happen, because then we're on the upslope. Some winters have none of those, and some have 2 or 3. Usually later in winter when it comes as snow if there is moisture in the area. Which my dogs love.

    Hope we get a couple of good, snowy FRO's this winter.


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