July 10, 2009

Thunderstorms

We have some potentially interesting weather coming up. But not tomorrow. Saturday will be beautiful...warm (into the lower 80s over much of the lowlands) and dry away from the mountains. Up in the Cascades there is a slight chance of some convective showers. But nothing serious.
And then there is Sunday. The air over us will be unstable, which means a little lift can release convection (i.e., thunderstorms). A measure that meteorologists look at to determine the potential for thunderstorms is CAPE--Convective Available Potential Energy. Sound impressive. Anyway, the values on Sunday will be high..particularly over the mountains (I have included a graphic of it that you can use to impress your friends). Normally we don't see CAPE of more than a few hundred here. But the CAPE tomorrow afternoon approaches 2000 over the northern Cascades, and over a thousand above all terrain. Something major is going to happen. In addition, an upper trough (which provides lift to release the instability) will move through on Sunday (see graphic). Between them, there is good chance of showers and thunderstorms over the mountains during the day and eastern Washington at night (see graphic of precipitation). Even a chance the lowlands could catch some of the action. Now a big worry is lightning caused fires...so we will have to watch this.

But wait! There's more! The trough will help incite an onshore push, which will bring cooler marine air into the region starting Sunday afternoon.

So enjoy a picnic tomorrow and enjoy the weather action on Sunday..particularly later in the day.

Also, If any of you are interested I will be giving a oublic talk in Leavenworth at 7 PM on July 31st and a book signing at 1 PM on August 1 (see more info to the right).

32 comments:

  1. Tomorrow will not be beautiful for all of us. Maybe I'll enjoy a picnic after the sun sets, when it gets nicer outside - or maybe later on Sunday!

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  2. would you explain the color code on the cape?

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  3. The Terminal Area Forecasts advertise 30% probability of Tstorms Saturday - you're not buying it?

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  4. I kind of miss the summer thunderstorms I grew up with in South Louisiana, but I don't miss the violent cells that used to pound us when I worked out in the Gulf of Mexico.

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  5. I do hope we get some thunderstorms in the lowlands! Fun! I miss them. Meanwhile, Cliff, what is the preferred place to find good weather forecasts on the web for the 3 Capes area of the Oregon coast (esp. for next weekend)? Many thanks....

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  6. Great news, Cliff! Sunshine and storms. A good assortment of weather. :)

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  7. Must read blogs asks "would you explain the color code on the cape?"

    The items on the plot are show in the top left corner: sea level pressure and CAPE.

    The color code on all of the charts is show in in the key at the bottom of the chart. The grey contour overlay is surface pressure. The color scale is increasing values of CAPE in J kg-1 (i.e. joules per kilogram) from white through purple then blue the cyan.

    Perhaps the more relevant question for you is "what is CAPE, really?" which this UK site gets it right

    http://www.weatheronline.co.uk/reports/wxfacts/CAPE---Convective-Available-Potential-Energy.htm

    Convective Available Potential Energy (CAPE) is measure of the amount of energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather.

    Thw wikipedia explanation is not bad (but a bit technical and not too well organized)

    http://en.wikipedia.org/wiki/Convective_available_potential_energy

    The higher the value CAPE the more the chance for thunderstorms and the more severe they will be (given certain other conditions so that you can actually generate rain).

    Interesting that the increased CAPE is showing across the northern Sound. Perhaps some interesting weather to the north of Seattle?

    The CAPE is pretty high in SW WA on Saturday too ... any chance of thunder there today?

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  8. The Lightning Ignition Efficiency is pretty good on the East side. Lets see how much moisture comes out of the cells. NO watches posted as of yet

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  9. Some of the leading edge of the system was visible Friday afternoon as some high level clouds and even some rain fell briefly around Portland. I'm hoping this next front brings in better tropo ducting on the VHF bands. The last few days haven't been too bad for lo-band DX.

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  10. All the CAPE around is in isolated small pockets of under 1000 J/kg. That's hardly anything, especially over just isolated little areas.

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  11. I have updated the CAPE map and added some more information. I saw some midlevel convective clouds this morning...cliff

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  12. The marine flow started earlier than usual today. It's getting really breezy at Salmon Bay. We're getting some notable northerly gusts. It's feeling a bit Kailua-Kona on our lanai.

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  13. We have some mid-level convective clouds over us right now that developed earlier this afternoon!:o)

    It has also been a nice, warm and summer like day. Here`s to more days like today with t-storms thrown in the mix.

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  14. Just heard some thunder here on BI. (8pm on Saturday) Big drops of rain to go with it - not enough to get everything wet, but interesting!

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  15. the marine push is here in chehalis.. aaaah its so nice it hit 90 today :(

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  16. SOUTHWEST INTERIOR-WEST SLOPES CENTRAL CASCADES AND PASSES-
    734 AM PDT SUN JUL 12 2009

    .NOW...SCATTERED THUNDERSTORMS ARE MOVING THROUGH THE SOUTHWEST
    INTERIOR AND WEST SLOPES OF THE CASCADES. WEATHER SPOTTERS IN
    THURSTON COUNTY REPORTED THUNDERSTORMS WITH POWER OUTAGES. EXPECT
    FREQUENT LIGHTNING WITH EACH STORM. SMALL HAIL UP TO HALF AN INCH IS
    POSSIBLE.

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  17. Had high based TSTM Saturday evening in the Lynnwood/Alderwood areas. Nice cloud to air lighting and virga.
    Timing was off by 12 hours.

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  18. Precip and a first peal of thunder over Capitol Hill at 10:50am.

    Looks interesting!

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  19. Cliff,

    Can you please comment on this: http://community.livejournal.com/seattle/5978626.html

    Was there rotation in the storm and was the structure actually a wall cloud?

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  20. Tumwater..first loud thunderclap at 7 am, off and on since then. A couple of heavy showers. Sometimes hard to tell thunder from the Big Guns being played with over at Ft. Lewis! Also got some pretty healthy sized hail at 1:50 p.m.
    I hope we get more thunder this afternoon..it is such a rarity around here.

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  21. we had a really good thunderstorm this am and twice more up until 11 am here in chehalis... i had alot of poofy kitty tails here!

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  22. Why do t-storms seem so much rarer in Bellingham than Seattle? Nothing here yet.

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  23. natchrl8r - My guess would be because of the strong maritime influence off the straight. I know this will sound like a cliché, but we did have more t-storms around here when I was growing up; mid 70s to mid 80s.

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  24. natchrl8r,
    I would be surprised if that was really the case. Perhaps Cliff knows the answer though, or has some data on the average number of storms at each location.

    I think the perception is that more weather in general occurs in Seattle because that's where the media focus is. You rarely hear about the weather in the north sound unless it's also affecting Seattle.

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  25. Big loud heavy freaking rain in Alki at 4:30 Sunday...Serious. And I was thinking of grilling...

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  26. There was a lovely sunset last night backing equally lovely lightning. Here is a photo looking northwest from University District; unfortunately the best shot of lightning I managed to capture: http://img44.imageshack.us/img44/6700/pict9522.jpg

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  27. Just starting to rain in Bellevue as I write this. Heard some thunder.

    I'm wondering why the smell of the air changes when it rains, especially during thunderstorms. Anybody know?

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  28. Does anybody know if there's a good evening adult education class on weather of the same caliber that Cliff posts here?

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  29. PRELIMINARY LOCAL STORM REPORT
    NATIONAL WEATHER SERVICE PENDLETON OR
    632 PM PDT SUN JUL 12 2009


    ..REMARKS..

    0615 PM FUNNEL CLOUD 6 E PENDLETON 45.67N 118.69W
    07/12/2009 UMATILLA OR AMATEUR RADIO

    HAM RADIO OPERATOR OBSERVED A FUNNEL CLOUD WHICH LASTED
    ABOUT MINUTES.

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  30. I would absolutely love to understand the weather in my neighborhood. I live in part of Sammamish near Sahalee. 1 mile north of my neighborhood, in Timberline, is wet and got rain. I'm sure if I got a mile south, rain there too. Though the radar shows rain over me right now, *nothing* is falling. It's kind of amazing in a spooky way. Works this way in winter too when snow comes up. We are in a strange little pocket of no weather and I'd love to understand why.

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  31. Athos,
    This is similar to the Bermuda Triangle, but for weather. The Sammamish Triangle. There are forces beyond our ability to forecast and understand...cliff

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