Saturday, June 6, 2020

More Thunderstorms and Showers Today, But Nothing Like Last Week

Another weekend, another thunderstorm--perhaps.

Some modestly unstable air is approaching the region and there will be showers from Puget Sound southward,how many will have the "juice" to provide lightning and thunder?

The latest visible satellite photo (7:12 AM)  shows a large fields of convective showers, produced by instability in the vertical,  over the Pacific Ocean (the showers are indicated by the "popcorn-looking features).   A star is shown over Seattle for orientation.


We can get an idea of how high these showers are (and thus their intensity) by viewing an infrared satellite image at the same time. This imagery shows the temperatures of the cloud tops, with taller clouds being cooler (see below)--the green colors are the highest. Clearly, some convective clouds--like cumulus/cumulonimbus-- out there, but right now none are producing lightning (we would pick that up with our lightning sensors).


All these instability clouds are there because two key ingredients are present:  upward motion produced by an upper trough (the match) and substantial vertical temperature change (the fuel), resulting from cool air aloft over relatively warm water near the surface.   The upper level map (around 18,000 ft, 500 hPa pressure) below shows the upper trough of lower pressure/heights right offshore.


Unlike last week, the trough is broad and mainly headed towards Oregon and northern CA, which will lessen its impact on western WA. And the instability aloft is not nearly as large.

The radar during the last hour shows the showers offshore, some of which are making landfall.



So what will happen today?   The unstable air air will head towards southern WA and Oregon and the instability will be enhanced by heating at the surface (like turning on your stove-top saucepan). 

The NOAA/NWS HRRR model predicts convective showers moving into western Washington and Oregon by 2 PM (see below--a simulated radar image at that time).


And the NWS HRRR model even tries to predict lightning threat (shown below), which does suggest a few lightning strikes moving into the region...but nothing like last Saturday.


The precipitation from the incoming showers today and tomorrow could add up in places, as illustrated by the predicted total rainfall through 5 PM Sunday. Not much over NW Washington and the Columbia Basin, but the western side of the Cascades and coastal Oregon gets plenty--up to 1-2 inches.  This is particularly good news for western Oregon and northern CA, which has been dry.



Now this all brings up a question that several of you have asked, why do we seem to be getting more precipitation over the weekends than during the week?    Some questions are beyond my ability to answer 😀.
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Announcement:

Online Talk:  The Mathematics of Weather Prediction, Sunday, June 7 at 1 PM.

I will be giving a talk on the how mathematics is used in weather prediction that will be available online (Zoom).  This is part of the "Math Hour" outreach of the UW Department of Mathematics and is directed to middle and high school students, but should be interesting and accessible to a wide audience.  If you are interested, you should register here

7 comments:

  1. Bit of thunder and lightning rolled though the Port Townsend area Friday afternoon.

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  2. yes, some in bellevue yesterday too. some heavy hail also.

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  3. I wonder where a likely good place to hike tomorrow might be, not rain free but some sun breaks.

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  4. Saturday around 5pm....a 20 minute furious burst of hail fell on Everett...very intense, and it left a beautiful, temporary coating of fake snow over everything!...then just rain for awhile...now 6:30, and more dark clouds are lurking around...I love the power of Nature!BTW, very little thunder...good call Cliff!

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  5. I made my way from Deception Pass to Seattle Sat afternoon -- winding ny way thru Mount Vernon, Bryant, Arlington, and Everett, among other spots. The convection I encountered was quite robust -- one dropped marble sized hail for more than 10 minutes, and another showed radar returns in excess of 70 db for a while over Everett. I don't know just how to compare it to last week's event, but any one of those cells would have been unusually strong for W Washington, and I personally experienced four of them in the space of two hours!

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  6. Has this been one of the colder May June's on record

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  7. Sunday night extreme thunder and lightning over Lummi Island, plus heavy rain. Spectacular and very unusual for any thunderstorms here. It was more like midwest storms! I'd love to hear about what happened.

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