September 18, 2021

Big Winds, Heavy Rain, and Now Thunderstorms

 Nearly 100,000 Washington State power customers lost power last night as strong winds first hit Northwest Washington and then spread across the remainder of the western interior as a powerful front crossed the region during the late evening.  Trees are very vulnerable to the first windstorm of the season, particularly if they are fully leafed out.

Winds gusted to around 60 mph over Northwest Washington, 40 mph over the lowlands of the South Sound, and reached 103 mph at Camp Muir on Mount Rainier.

The power outage map from Puget Sound Energy last might shows the damage, centered around NW Washington and the south Sound towards the Cascades.

Here are the top wind speeds on Friday (click to expand).  A gust to 63 mph a Whidbey Island Naval Air station, nearly the same at Port Townsend, and nearly 50 mph on the San Juans.   These winds occurred during the afternoon before the front made landfall.   

Strong winds over NW Washington are very typical for winter weather systems around here,  with the powerful winds responding to the strong pressure difference (gradient) produced downstream of the Olympics.  This is illustrated by the forecast pressure (brown lines are isobars, lines of constant pressure) and winds (color shading) at 5 PM yesterday (below).   Look carefully and you will see a large change of pressure over northern Whidbey Island....this accelerated winds from the southeast.

Over the south Sound, the winds gusted to 40-50 mph last night over the lower elevations, 70-80 mph on lower peaks, and over 100 mph on Rainier.

These winds occurred during the later evening as the strong front went through....the feature I warned about in my last blog.  The radar image at 11:11 PM last night showed a line of strong radar return with the front (the arrow shows you the feature).

The frontal winds came up very quickly and dropped very quickly, as illustrated by the winds at the USDA RAWS site in Enumclaw, southwest of Seattle.  A gust to 36 mph with the front.

And this was a particularly strong front with a VERY large temperature change associated with it.  To prove this, here are the temperatures at Enumclaw.  Temperatures rose before the front to 72F and then crashed to the lower 50s within a few hours.  Don't see that kind of large temperature changes with fronts very often around here!

Precipitation?   This system brought plenty, ranging from 4-6 inches in the mountains to around a half-inch in the rain shadowed areas.

Rivers are way up right now, with many Washington rivers above normal levels.  But no flooding because they started at below-normal to normal levels.   

Part II. Thunderstorms and showers

The excitement is not over yet!  With an upper-level trough/low approaching and cooler air moving in aloft, the atmosphere will be primed for convection and thunderstorms.  So get your lightning rods ready.

The latest visible satellite image shows the front moving through right now (the solid band of clouds) but also displays lots of convection (instability showers of cumulonimbus) offshore (these are the popcorn-appearing features).  Those showers are strong and have our names on them.  But most of you will have a break this morning and early afternoon--so have fun outside this morning if you can.

A particularly potent band will come through this afternoon and evening (see the simulated radar image at midnight tonight below).   Many of you will hear the rumblings of thunder.  And more shower action on Sunday.  

It is good to have active weather back...and I note that it is quite typical for this time of the year.

Forecast radar reflectivity at midnight tonight.


  1. Noted yesterday afternoon after I took time before the rains hit to get bread and make a quick run to Winco for peppercorns, so the Franz bakery outlet out near Parkland off of Pacific Ave and the Winco off of 72nd near I-5.

    Anyway, came out of Winco to blustery winds, but still dry and hoped to capture the showers that came through last night, but they waited until after I went to bed. Awoke to no showers at 5AM this morning but obviously it had rained, and my covered deck on the NW side of my house was all wet as the rain was driven well inside the space. So this morning I'll make a quick dash out back to put my plastic chairs away as one kept blowing off the deck as the winds blew from the west and stick them in the shed.

    I, in anticipation took down my tomato plants the other day as one, they were an heirloom variety were slowing down as the temps had been dropping occasionally to the upper 40's and the highs in Tacoma only hitting the mid to upper 70's and with these rains, time to just pull 'em.

    Have tomatoes to ripen in the kitchen now.

    I thought it was on the warmish side yesterday afternoon and no wonder, with the temps shooting to the low 70's before dropping.

    I recall one year, I think in the early 80's a Pineapple express storm hit the area and the temps were quite mild, mid 60's during the height of the storm.

    I do recall another one while at an episcopal church conference At St Elizabeth's in Burien and can't recall if the storm was present as we all gathered at the church around 5-5:30PM on Friday, but it whipped up during the evening and through much of Saturday with major winds, a power outage, thunder and lightning, the whole nine yards and Saturday evening, much of Burien was without power, but the church as it stayed lit the whole time. Storm had passed by, by Sunday morning. This was in October if I recall.

    Will try to get footage for a video of the storm later today as I already have some footage from yesterday.

  2. Here in Grants Pass, 1.15" since early this morning.

    1. Update: storm total of 1.52". That's substantial for the Rogue Valley in mid-September.

  3. This storm has been a complete bust east of the Cascades. Very disappointed

    1. Sorry for your loss. We were expecting steady rain here in Tacoma, and…. Well, noon Saturday and just a couple of good showers overnight. Not saying Cliff is wrong or nothin’…. But, like they say, you don’t like NW weather, wait five minutes. We Will Get Moisture, falling from the sky. (The Freemen look up and say, Moisture falling from the sky….)

    2. Well I’m happy to report I spoke to soon...we’re now up to a storm total of 0.80”

    3. @Sid got DUMPED on here in Tacoma this weekend Saturday & Sunday.

  4. It's now 2:19pm and the rain is falling as I type, and it's staring to come down good now in Tacoma. We had the rain last night for those that missed that. I saw evidence of that this morning and it's now quite wet out there.

  5. I was really surprised at the temperature spike last night as the storm came in. Then the rain hit and here on Capitol Hill it maxed out at 1.04”/hr for a couple minutes. I got a kick out of seeing my Davis Instruments weather console flashing “It’s raining cats n dogs”. Old Harry W might have been going for pigs n chickens at that point.

  6. As usual, it seems that the Rain Shadow once again spared us with the more dramatic effects of the storm...I waited in vain for some thunder action here in Everett!...Winds were not overpowering, etc. According to stats, W. Wash should experience seven T-storms per year...I have only witnessed one brief episode this year, so far!

    1. Yes, it usually disappoints me. I did not see any either. I think the official definition of "thunderstorm day" requires only that thunder be heard at least once on that day. A real show only comes once every 2-4 years here in the Puget Sound Basin (for example, Sept. 2019 and May 2017). Perhaps a better measure of thunder and lightning excitement is a map of the number of "flashes per square mile (or per square kilometer) per year", and such are available. It looks rather different from the map of "thunderstorm days" per year, and it makes the Northwest look even worse, relative to the rest of the country.

  7. Cliff your model did a good job showing the rain shadow in the Okanogan Valley. Just north of me go a bit of a shower, but nothing of consequence. NWS spokange issued flash flood for Okanogan County, so many didn't believe me when I said we would get little to no rain unless a thunder cell came over. Seeing any event in near future that would bring moisture from the south? Would love to see some rain here.

  8. In North Seattle, where I live, I would have called this a bust except for yesterday's massive squall we had. An incredible amount of rain fell in a short period of time late in the afternoon. We had very little rain Friday.

  9. You nailed the forecast Cliff, thanks again for all keeping the public informed. This system just didnt want to give up, out here in N.Bend it was still pouring at midnight on Sunday with red/yellow on the radar. Seems like a convergence zone set up south of Route 2 and then migrated south to I-90 before finally letting up. Looking forward to many more storms over the next several months after the somewhat "boring" weather this summer :)


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