September 02, 2016

First Major Convergence Zone of the "Fall"

Today was a wet day around Puget Sound, with some locations getting as much rain in the last12 hr as all of July and August.  The reason?  An upper trough passage with a strong Puget Sound Convergence Zone.  There was torrential rain, lightning and thunder, and even a report of funnel cloud.

 Here is the 12 hour total ending 7 PM Friday for rainfall from Seattle Rainwatch.  A huge gradient of rain from virtually nothing over the south Sound to as much as 2-4 inches within a southwest-northeast band.

This band was mainly associated with our local favorite weather feature, the Puget Sound Convergence Zone, which is produced by converging airstreams over Puget Sound.  Converging air causes upward motion...and with relatively unstable air aloft...lots of convection and thunderstorms.  You could view the convergence zone in action from this radar image around 3 PM.  You see the band over Puget Sound?  Red colors are pouring rain or hail.

During the same period, the lightning detection network showed similarly oriented lightning activity.

The SpaceNeedle Cam got a good luck at the scary looking cumulonimbus clouds associated with the convergence zone.  Here is at image around 3 PM looking north.  You can see the precipitation falling out of the clouds.

A visible satellite image around 2:30 PM shows the convergence zone and the characteristic dry zones to the north and south (caused by air sinking off the Olympics and Vancouver Is. mountains.)

The western slopes of the Cascades and Olympics also received plenty of rain today as shown by the 24 rainfall totals ending 8 PM Friday.  A few favored locations (east of Monroe) got washed away with 2-3 inches.

The summer drought is over..... we will miss it.

Announcement: My Climate Surprise Talk on September 28.

During the evening of September 28, I will be giving a talk in Seattle at UW's Kane Hall on Climate Surprise: Unexpected Impacts of Global Warming on the Pacific Northwest.   You think global warming will simply bring warmer temperatures, drought,  less snow, and more storms?  Think again. The latest climate model simulations provide a far more nuanced prediction of what will happen here, with some of the results quite surprising.   This talk is sponsored by CarbonWa and the Audubon Society To find out more or to secure tickets, please go here.


  1. As you said, there was virtually no rainfall in some areas - or no rainfall at all in the case of north Whatcom County. So you probably want to qualify your "end of the summer drought" proclamation. There is life beyond Seattle.

  2. Your analysis of the weather is admirable. Since May, the seasons seemed to be about a month ahead (regarding farming and produce). Even the trees in the area were dramatically showing their fall colors in August. In regard to your global warming comment: it is nice to finally hear someone clarifying that global warming doesn't mean lack of snow, drought and a temperature incline. When I was working on my geology degree back in 2004, we regarded global warming as a period of meteorological disturbance with increased weather phenomenon like colder winters, seeing snow further south and going as far as entering a micro ice age as the climate tried to balance. I look forward to reading more of your ideas on this subject and looking forward to possibly seeing some snow this year in the Puget Lowlands...maybe.

  3. Colleen: Wow, all you have done this year is complain. No snow, no rain, no this no that. Maybe you might consider moving elsewhere because you just might live in the most boring weather county on Earth! (sarcasm). This has been a great summer in Central Washington. Some heat, some normal temps, some cool temps and plentiful sunshine. Rain the last two days and a chance mid week, temps in the 70s. Might I ask, but do you have a positive comment ever to add here or just complain? There is also much life beyond Whatcom County!

  4. I found a full 1.5" of water in a plastic tub in my yard in Kirkland, well away from trees or anything else that could affect capture. Now THAT was some serious rain! My rhododendrons, whose leaves were limp and curled from drought, are now lifting them joyously to the sky.

  5. About .75 inches in my rain gauge at the admiralty inlet... Cut the dust a bit. Nice! Insanely perfect day today.

  6. What a rude remark, MRT. There is indeed much life beyond my backyard, and yours, and Cliff's. I was responding to the discrepancies in Cliff's post: noting that some areas received no moisture, and yet writing that the drought is over. No need to get worked up. Have a great week.

  7. Colleen: Than don't post complaints about where you live all the time, complaining. Actually add to the discussion in some positive way, not negatively. I call people out on this blog and I am calling you out on past comments. Where we live is where we live. We can't control the weather and I know from personal experience that I have complained too much about it and won't these days because it makes no difference. It can snow 10 feet if it wants to, or rain hard, or be hot for weeks in a row, or cold for weeks in a row, doesn't matter. The point that most people are not getting on this site is that the blog is for talking about the increase our understanding of it. Not complain about the weather, but understand it. My whole point was not to get so stuck on one thing, Whatcom County, that you can't see what is going on around the PACNW, the country or the world, weather wise.

  8. I got a pretty decent thunderstorm on Saturday. As of today, 2.25 inches of rain on the Bothell-Mill creek line.

  9. I forgot to say, 2.25 inches so far this month.


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