Saturday, February 1, 2020

Cold Air is Surging Into the the Northwest

After a period of wet conditions with far above-normal temperatures, much cooler air is flooding into the region behind a Pacific cold front.

The latest visible image from the GOES-17 satellite clearly shows the story, with the long cloud band of the front  just starting to exit western Washington, while cold, unstable air (indicated by energetic convective activity--indicated by the popcorn looking clouds) is found offshore.


The current weather radar imagery below, illustrates the weakening remnant of the frontal precipitation, now over Oregon.  Behind the front, a Puget Sound Convergence zone has formed north of Seattle.  You can see some of the cold, instability showers moving in over the coast.


This cold, unstable air mass, with lots of convective showers, should drop the temperatures by 10-20 degrees during the next day....already temperatures around western Washington are in the 40sF, after climbing into the mid 50s yesterday.   The snow level will decline to roughly 500 ft, so the higher hills may get whitened and don't be shocked if a few wet snowflakes get mixed in later today and Sunday.

The mountains are now changing over from rain to snow and the predicted accumulated snow total over the next 48 h (through 4 AM Monday) projects as much as 6-18 inches in terrain.  Some lowland areas (e.g., around Bellingham and the coast) may get some very light snow. 


Importantly, the road surfaces are relatively warm after the recent mild weather, so snow should melt quickly if it falls.  This air is not as cold as the previous event and there is no active surge of arctic air through the Fraser River Valley.

Finally, this winter so far has been one of extremes.  We start dry, then go wet.  And we have alternated between warm and cool periods (see temperatures at Sea Tac for the last 12 weeks, below).  A bipolar winter, which perhaps might reflect the national mood about other things....



13 comments:

  1. Bipolar! That really does sum up the overall atmosphere these days.

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  2. Thanks Cliff. As always enjoy your humor at the end of the posting.

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  3. It was 64° yesterday here in Sequim at 18:00, and possibly the warmest spot on the West Coast north of the Bay area at that hour. My records show it to be the warmest January temp in the past 10 years for "the blue hole”.

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  4. Bipolar for sure!
    Love the quick, smart reads.

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  5. Even though there has been a lot of volatility, as far as average temperatures go, it has been quite warm this winter. For January at SeaTac, the average high was 49 compared to a normal of 47 and the average low was 41 compared to a normal of 37. Differentials for last November and December were in the same ballpark. And even with these rather notable rains, for the current water year, most locations are at about normal levels, with Quillayute being the main exception. Snowpack in the northwest is about at normal levels now.

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    1. Caught up to normal after the dry anomaly from late October to early-mid Nov.

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  6. Cliff,

    I like your major weather feature labels within the images! It's a good way to practice reading what is happening.

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  7. Wow! Gotta love sequim for the rain shadow! Hopefully there was sun as well. I grew up in Kingston and we would drive to Sequim “for fun” to see the sun!

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    1. Don't worry, we have seen several feet of snow up in Sequim before. Places in Pierce County misses out the most and no convergence zone

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    2. Sequim resident here, been living on this side for a better part of a decade now, and can definitely remember the winter of 07. CHILLER!

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  8. The dramatic weather change yesterday at Stevens Pass was as predicted: Heavy rain, high winds and very warm temperature until about 10:15 a.m. Then the temperature and the wind dropped and it started snowing. The Skykomish was raging and flooding in several communities. Don't be a flood tourist! We watched some foolish people climbing down a sodden bank to get photos of the river, which was tossing fallen trees around.

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  9. We woke up with snow in Bothell

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  10. Walter Kelly of Q 13 news keeps warning us that February is our coldest month. I'm pretty sure that's wrong- I looked it up on 2 different sites...

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