October 07, 2023

The Last Summer-Like Weekend of the Year

One of the burdens of writing this blog is the necessity on some occasions to describe some unpleasant meteorological facts.

And this is one of those blogs.

Today was wonderfully warm and dry, and tomorrow will be almost as good.   

But this weekend represents the high point of our autumn-- a return of such perfect conditions is highly unlikely for the rest of the cool season.

But before I discuss the big cooldown, consider today's wonderous high temperatures (see below).  Upper 70s and lower 80s over western Washington, and low 80s over much of the Columbia Basin.


The origin of this delightful period?   A ridge of high pressure aloft (see 500-hPa pressure map..around 18,000 ft) for this morning at 5 AM.


Monday morning the ridge moves out and rain and cooling moves in.   Take a look at the extended temperature prediction from the NOAA National Blend of Models for Seattle (below).  Tomorrow is the last day that will rise into the mid-70s over the next 10 days-- a period in which the sun is weakening rapidly.

   
The highly skillful European Center ensemble of many forecasts shows a similar pattern (through October 21)


Why can I be so sure that we won't get into the mid-70s and 80s after this?  
Climatology 

Take a look at the climatology of SeaTac Airport from Oct 7 to November 25.  The red shading shows record highs.  The blue shows record lows.

The sun is strong enough to get into the upper 70s and even into the 80s through mid-October.    But temperatures have NEVER gotten into the 80s after that.  In fact never into the upper 70s.


The next ten days should be quite wet, with total precipitation exceeding 3 inches in most of the coastal terrain of Washington and SW British Columbia.  Time to check on our rain gear!


Sorry....

3 comments:

  1. No need to feel sorry!...I love our gradual cool-downs during this time of year...our special doses of "liquid sunshine" make for all of the beauty we enjoy by living is this moderate climate. Fall is so impressive here!...This a.m. I sat in my SUV, in my driveway, enjoying a cup of coffee, and taking in the various Fall colors taking over my tree-lined neighborhood. It felt like I was living in the middle of a gorgeous post-card!...it was almost a "Zen" moment!

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  2. On the final image, there is a thin band (blue color; .75 to 1 in.) that runs from B. C. into California. My location is in that area. It is not the driest place in WA, but had I known this 35 years ago we could have moved to a place 10 miles west and into a bit more precipitation. [Gardening; more trees; etc.]
    The isohyets are close together here.

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  3. Interesting cloud appeared to originate from Summer Lake, Oregon this afternoon. Looked like a forest fire plume, eruption, or convergence zone. But over the Alkali lake, those seem like non-starters. Could it have been some sort of wind transported cloud-seeding like ship tracks?

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