October 22, 2014

Heavy Rainfall, Eclipse Weather, and Possible Saturday Windstorm

Today we had an active atmospheric river over western Washington and Oregon, producing some impressive one-day totals.  Take a look at the total precipitation for the 24-h period ending 8 PM on Wednesday (see image).  Some locations (such as near the SE side of the Olympics) have reached over 4 inches, while 2-4 inches was widespread over terrain.  Only portions of eastern Washington received less than .05 inches.

The 24-h rainfall amounts from Seattle Rainwatch, based on the Camano Is. radar, shows a huge contrast in western Washington, ranging from 2-3 inches in the southern Sound to roughly half that north of Everett.
An infrared satellite picture at 1 PM his afternoon shows the plume of moisture extending into our region, and lots of unstable air behind it over the Pacific, which will be moving in tomorrow.

The partial solar eclipse

A partial eclipse of the sun will occur tomorrow (Thursday) afternoon starting at 1:36 PM and ending at 4:20 PM here in Seattle.  Will it be clear enough for you to see it?

Here is the UW WRF model's cloud forecast for 3 PM.  Best place to go for a chance for clear skies?  The eastern slopes of the Cascades.

And finally, I and others have been watching the potential storm on Saturday.  The solutions have shifted a bit, but right now it looks like we will have a decent blow on Saturday night, but not an historic windstorm.

On Saturday at 11 AM, the pressure forecast shows a strong, but elongated low off the Washington/Oregon coast.  Elongated is not good...you want a compact, concentrated storm.  But there are large pressure gradients along the northern CA and southern Oregon coasts--40-60 mph gusts are possible
 By 2 AM on Sunday the low has passed into southern BC and a large pressure gradient is over western Washington.  Expect wind and some power outages, particularly since leaves are on the trees.  Still plenty of uncertainty with this storm, so will watch it carefully.


  1. You mentioned 24 hour rainfall.

    Do you take advantage of the CocoRaHS network of measurements?
    ( they seem to measure 24 hours from 7AM to 7AM, but I think you are getting data from midnight to midnight, right? )

  2. 1.44" here in the Alderwood Maor area of Bothell.

  3. It looks like the two lows off the coast may be merging. One is a 984 mb and the other is 986 mb; both quite low. If they combine would that cause even further deepening and create a meteorological "Bomb"? There is also another low approaching those two from the north which currently measures 997 mb. Interesting.

  4. Off topic, excellent evening to watch the bird migration from the Canadian boarder through the Willamette Valley on the UW weather radar.

  5. Tornadoes. Two in two weeks. Care to comment?

  6. Just wanted to thank you (a little late) for your eclipse viewing advice, which served me so well.

    I left Bothell later than planned in a surprisingly-long sun break headed for Wenatchee. When I got to Gold Bar I realized I'd miss the start if I continued on, because it was sunny where I was and the clouds were increasing ahead over the mountains of course and I wasn't going to make it to clear weather on the eastern side in time. So I set up my telescope (with solar filter) in Gold Bar and got thirty minutes viewing of the eclipse start and the tremendous sunspot system (as big as Jupiter, reportedly). As clouds blew in, I continued my drive and stopped in Leavenworth in time for the maximum eclipse point. Leavenworth was just on the edge of the cloud bank clinging to the mountains. Clouds finally rolled in and blocked my view for good at 4pm, twenty minutes before the lunar egress, which I was disappointed to miss. C'est la vie!

    I was toying the whole time with decamping to a spot further east, but I could see a persistent band of very-high clouds running NE-SW that I thought might block my view if I moved to Wenatchee. I thought this might be caused either by the jet-stream or a front from the low pressure system.

    The change in weather on the drive back was astounding to me, with such heavy rain west of Stevens Pass. We really need to build some more hydro-electric systems to make use of all that energy (if we can do so in an environmentally-friendly way).


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