Thunderstorms Possible For Some Wednesday PM & Evening

June 19, 2018

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.

500t.36.0000

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:

olr.39.0000

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