Thunderstorms Possible For Some Wednesday PM & Evening

7pm Tuesday…

Today was a warm one, we hit 91 in Portland, our 3rd 90 degree day so far this season.  Let the annual 90 degree day count begin…

90 Degree Days Summer Heat

Tomorrow the atmosphere overhead warms slightly, plus we don’t get any cooling onshore flow until after 5pm.  That tells me we have a good chance of hitting 90, but it all depends on thunderstorm cloud cover.  If it arrives by 3-4pm we’ll stay in the 80s.

Speaking of thunder…the weather pattern tomorrow screams THUNDER ACTION to this weather geek.  We have a perfect setup for Cascade thunderstorms to spread down into portions of the western valleys of NW Oregon and SW Washington.  An upper-level “wave” moves overhead.  Note the southerly wind flow at 500 millibars over us Wednesday.  That’s around 18,000′ up.  The little kink in the lines in SW Oregon shows the disturbance moving up through Western Oregon.  There is plenty of lifting ahead of it.


Models are all in agreement showing Lifted Index well below zero (lots of instability). Lots of moisture will be available overhead with precipitable water up around 1″ or more.  That’s a juicy atmosphere.  Lots of CAPE available as well

RPM CAPE Forecast

The WRF-GFS is showing a nice blowup of storms between 1-8pm…here’s the simulated satellite pic at 8pm:


Storm Prediction Center has the central part of our state under a marginal risk for severe thunderstorms

USA_ConvectiveOutlookDay2 Only.png

To summarize:

  1. Thunderstorms will develop over the Cascades early-mid afternoon tomorrow. Some could become quite strong.
  2. Sometime after 3pm they may move out into the valleys, or just develop directly over the valleys.  Anyone from the Coast Range east could see a thunderstorm, but they will be scattered and not everyone will see one.
  3. Storms will be slow-moving which means some of us could get a huge soaking, while 5 miles away it remains dry.
  4. Storms should be ending after 10pm as a strong push of cool marine air arrives west of the Cascades.  Thursday will be mainly cloudy and up to 20 degrees cooler!


I’ll be here all afternoon/evening tomorrow and we’ll be on the air of course from 5pm onward.  A rare busy summer weather day in the Pacific Northwest!

Chief Meteorologist Mark Nelsen


46 Responses to Thunderstorms Possible For Some Wednesday PM & Evening

  1. W7ENK says:

    Hey, guess what?

    KRTX radar just went down!


    • Ryan (Walnut Grove) says:

      Of course it would… Though Radarscope still shows it as up.

      I wouldn’t be surprised if it crapped out today though.

  2. W7ENK says:

    354 PM PDT WED JUN 20 2018

    • Ryan (Walnut Grove) says:

      Which is awesome if you are in the Cascades….

      So far everything that has popped up on the radar is east of the crest and drifting NE.

      No dice in the valleys so far.

  3. W7ENK says:

    342 PM PDT WED JUN 20 2018

  4. Ken in Wood Village says:

    I’m in Welches, OR now. I took a pic but it uploaded sideways, sorry

  5. W7ENK says:

    308 PM PDT WED JUN 20 2018

  6. Ryan (Walnut Grove) says:

    So far everything is poping east of the Cascade Crest. I am seeing CU in the coast range, SE Clark County, along the foot hills east of the metro, SE of the metro… Nothing forming over the metro yet.

    I’m lowering my expectations for the moment.

  7. K says:

    A Significant Weather Advisory was just issued for a strong storm near Mt. St. Helens.

  8. K says:

    Projected CAPE values are crazy high. They might be higher than 5/4/17 (someone please check that).

    • Ken in Wood Village says:

      I don’t remember what the CAPE was back then but I want to say they are about the same or higher. I’m going to head out to Sandy, OR in a little bit. The convection is crazy right now.

      • K says:

        Ooh, have fun! Post videos if things start to get crazy (my gut feeling is that they will).

  9. Ken in Wood Village says:

    I was driving home from being out visiting friends and I looked towards Mt. Hood, some of the clouds have anvil tops. Things are getting interesting out there 🙂

  10. Roland Derksen says:

    We’re seeing a chance for showers (or thundershowers) up here as well. Probably won’t amount to more than a distant rumble or a sprinkle, but we’ll see.

  11. Tanis Leach says:


  12. Jason Hougak says:

    Mt. Hood has some convection starting to build up.

  13. paulbeugene says:

    Last couple runs of HRRR keep any west side convection south of PDX metro through the evening…with Corvallis through Salem getting some action.

  14. Jason says:

    If I wanted to go see a thunderstorm this evening where / when would be the best place to be? Maybe Sandy area and east of that? Silverfalls area?

  15. Ken in Wood Village says:

    Wow, Crown Point is already up to 81F 🤔

  16. paulbeugene says:

    This isn’t June 4 2009. That is the Columbus Day of convective outbreaks of this type

  17. Ken in Wood Village says:

    I think everyone should read the area forecast decision from the NWS. It’s very interesting and good for our area

  18. paulbeugene says:

    Looks good for convection in north Willamette Valley. As usual, south valley tends to miss out on surface based convection in this pattern with marine layer coming in early.

  19. Jason Hougak says:

    Need another update Mark
    We are bucking hay later today and would be no good to have it get wet!

  20. runrain says:

    Also, note that we’re 8 deg higher at 8am than we were yesterday.

    • Ken in Wood Village says:

      I know what you mean. Troutdale is already up to 72F which is much higher than yesterday. The DP is 59F and Humidity is 65%

      I think it could be very interesting today 😉

    • Paul D says:

      It is cookin’ out there already! 77 in Hillsboro.

  21. pappoose in scappoose says:

    When thunder roars, get outside!

  22. Ken in Wood Village says:

    Hmmm, interesting

  23. Larry says:

    This should be an interesting afternoon!

  24. K says:

    I’ll be keeping an eye on things tomorrow. Maybe my weather station will pick up something. Here in Pune, India, CAPE values are predicted to be between 1500-2500 j/kg later today. Perhaps some thunderstorms here.

  25. Brandon says:

    SPC shows marginal risk for the metro area now

  26. I should call in sick and do some storm chasing tomorrow….

  27. Paul D says:

    Thursday looks awesome! Will be nice to get back to normal for June.

  28. JERAT416 says:

    Bring on the strays, this time further west!

  29. Muxpux (Castle Rock) says:

    Sounds like you should be gearing up those fox12 cams for timelapsing tomorrow…

    Judging by past experience, I’d guess the onshore flow will seep up the Columbia into Kelso just as the storms arrive, effectively killing them. Same thing that happened June 4th 09

  30. Ken in Wood Village says:

    Sounds like storm chasing tomorrow 🙂 First

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