September 27, 2013

Weekend's Big Weather Event

I will have an update nowcast at 10 AM Sunday....

I spent my early evening getting my home ready for the onslaught....and by day break the rain will have overspread the region.

The new 4-km WRF model run is the same story as before :  heavy rain from two major pulses on Saturday and Sunday.  Here is the 72 hr precipitation totals over the Northwest.  Much of the terrain will get 5-10 inches, some of the higher peaks more.

Let's zoom in over western Washington.  What a contrast!  More then 10 inches over the higher Olympics, while about a half inch over Sequim.  A factor of 20...amazing.  In Sequim on Saturday there will only some light rain.  Over Puget Sound there will be a strong north-south gradient in precipitation...a lot more in Tacoma than Everett.

Now, there is a another threat that must be mentioned.  A small but intense low center will form on Sunday over the Pacific and will move northeastward, crossing somewhere between the Olympics and central Vancouver Island.  Here are two solutions for Sunday at 8 PM.  The UW NAM-MM5 has the low over Tatoosh,  Big threat of strong winds over Puget Sound.

While the WRF-GFS takes it a bit far northwest.  Both bring strong pressure gradients and strong winds to the coast, which you can expect 40-60 mph gusts.
 The WRF surface winds for this time, show sustained winds of 35 kts (40 mph) along the coast and over the interior waters of NW Washington. Gusts would be considerably higher.

Enjoy the weather show.   Not a good day for a hike.


  1. Thanks for the update Cliff. I'm up late watching the radar as the rain moves inland to the Puget Sound area. I'm really looking forward to this event!

    -Scott K. (Auburn, WA)

  2. Thank you so much for your updates . I come here for my weather information rather than the local news. You explain it in a way that makes me want to learn more and more about weather.

  3. 3/4" so far (10:30a Sat.) here at Thornton Creek retention pond. The intake for the diversion structure leading overflow directly to Lake Washington was revised this past summer as part of a large, multi-year effort to mitigate recurrent flooding of Nathan Hale, homes downstream of Thornton Creek pond. Not enough rain delivered fast enough to properly test it, yet.

    Next year's installation of the what we locals call the "mega-swale," taking out the insane right-angle boxed convergence of Thornton N and S forks as well as easing banks adjacent to NH sports fields should produce a big improvement in surge handling, at according to the design.

    Strangely enough, even though the creek is at the end of our backyard and the house is not elevated our own problem here has always been groundwater as opposed to direct invasion by the creek (so far, knock on wood).

  4. 1.19" in Sammamish so far. Wind is blowing in the 10MPH range with gusts (at the rooftop) of 15MPH.

  5. Just home from the Husky game. Whoa. Wettest game I've been to in over 40 years of going to games. Arizona couldn't find a spot in the Southwest to prepare for the likes of this onslaught. My barometer seems to have bottomed out at 29.19 (ya, it's very old but an heirloom, and I love it) and my rain gauge has 1.25 inches in it since this morning at 8:00a.m. I can't remember a September to match this one and I've been here since 1949.

  6. 1.28" at our house in Bellevue so far... and our power was off for four hours, thanks largely due to the windy conditions, I suspect. I hope tomorrow's not windier, or that the PSE repair holds!
    Any chance you'll do any nowcasting this weekend? I always enjoy it when you do that, and appreciate your so far spot-on predictions about this stormy weekend.

  7. ~1.8" for the day here in Meadowbrook.


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