July 29, 2017

Superheat Coming to the Northwest This Week

If you were thinking about buying a fan this summer, I would hit the stores soon.

If you were thinking of picking up an AC unit, I would take care of that right away.

Big heat is coming to the Northwest later this week, with record breaking temperatures for many, particularly on Thursday, the warmest day.  We are talking about mid to upper 90s F around Puget Sound, and 105-110F near Portland.

During mid-week, a huge ridge of high pressure will build over the western U.S. (see upper level map--500 hPa level--for 5 PM Thursday).

The WRF forecast surface pressure map (with lower atmosphere... 925 hPa, roughly 3000 ft.... temperatures) shows the classic heat wave pattern, with low pressure (thermal trough) extending into western Washington and easterly flow over Cascades.

Take a look at the 5 PM Thursday surface air temperatures (at 2 meters) forecast by the UW WRF model (below).  Mid to upper 90s around Puget Sound (cooler right next to the water) and  over 104F across SW Washington and the Willamette Valley.   I need to change the temperature scale for such heat waves!

Weather.com has excellent forecast and they are going for 95F at Seattle-Tacoma Airport and an AMAZING 110F at Portland.  Keep in mind that this would be higher than the ALL TIME MAX temperature at Portland (107F).



But how confident are these forecasts?  What are the uncertainties?   

As I have described many times in this blog, one should turn to ensemble forecasts (running the model many times with slightly different initial conditions and physics).   Let's start with the best ensemble system, that of the European Center, for Seattle Tacoma Airport.  Their single high resolution forecast is shown by the black line, the mean of the ensemble by the green line, and the spread of the ensembles by the whiskers and green boxes (the whisker are the extremes of the ensembles and the boxes show you the 50 percent of the forecasts closest to the median).

On Thursday, the high-resolution (deterministic) forecast is going for about 97F and the ensemble mean is ABOVE 100F!  Crazy warm.

The US GFS ensemble is peaking around 96F and all the members are very warm.  But one good thing...temperatures will cool down into the 60s at night, so with a good fan you will be able get your rooms cool enough for sleep.
The bottom line of all this information is that we have great confidence of a major warm up, with Thursday heading above 95F. I suspect several locations in the eastern suburbs of Seattle will hit 100F.   And SW Washington, Portland, and the Willamette Valley will exceed the century mark by 5-10F.   And the ensembles show the potential for even warmer conditions.

On second though, perhaps you should run to buy that fan tonight....


  1. Time to battery up the old face mister fan.

  2. I dont mind the heat as long as the nights cool down enough. Still no rain in sight and the GFS which had a glimmer of hope for some rain in the longer range on the 00z run now is bone dry as far as the eye can see.

  3. I'm not buying more than 95-6ish on Thursday. Usually Seattle avoids the century mark in heat waves such as this. I'm also praying for 38-42 degree dew points and a week of highs barely hitting 70 in the week after with even rain on Monday! That's all I'm wishing for. I don't want a fan making noise all night.

  4. Got the AC unit into the apartment today. Going to need it bigtime here in the central Willamette Valley where we will likely break our all time record of 107F.

  5. Thanks for the heads up and excellent explanation. I really enjoy knowing "why" the weather is doing what the heck it is doing.

  6. I always wonder if people who love these heat waves have air conditioners at home and work. Because the heat is hard on people who don't.

  7. Is there a record of daily highs for the month of August such that we could have a distribution and see just rare Thursday might be?

  8. I have an air conditioner unit in the wall of my house. I've lived here for 10 years and used it twice. I have air conditioning in my car. I roll with the windows down. i don't have air conditioning at work. i just work....more slowly.

    i like the heat waves, and i do empathize with those who tend to overheat, but it's only a few days! you'll sweat a little, you'll be uncomfortable, and then it will be over. you'll be fine.

  9. how about a status update on that upcoming el nino

  10. I might be fine, joe mama, those around me not so much...when it doesn't cool down at night, I don't sleep well, even with AC (due to noise) and I get VERY crabby.

  11. Cliff - Is it possible for the Northwest to generate enough heat/low pressure that it pulls monsoonal moisture up from the Southwest?

  12. I'm ready, I turned down the hot tub temperature so that it is now a cool tub.

  13. Joe mama,

    Heat waves may be pleasant for you, but they are the most lethal type of weather phenomenon (at least 400 deaths and 6200 hospitalizations annually in the U.S.) and you can be sure, regretfully, that people (especially children and the elderly) and pets in the Pacific Northwest will suffer and possibly die because of the heat over the coming week.

  14. So how many weeks will this 'blob' last?

  15. Here comes the smoke! A distinct wildfire smoke smell in Langley in the past hour (smells like its not local smoke). Yesterday I saw a small smoke plume on the flanks of Mt. Pilchuck, but I can't find any information about it on news sites or the official fire sites. There is a fire burning near Darrington though. W. Washington forests are very dry right now...I hope everyone heeds the advice of Smokey Bear over the next month.


  16. "Kept a chance for thunderstorms in the Lane County Cascades on
    Saturday and Sunday as a shortwave trough rides up the back-side of
    this upper-level ridge over the area. This shortwave will
    destabilize the atmosphere and possibly bring enough moisture for a
    couple showers and thunderstorms in the Lane County Cascades. -McCoy" NWS Portland

    From personal observation I have noticed that in Portland when the heat low moves inland, this seems to be the greatest chance of thunderstorms in the Cascades and Willamette Valley.

  17. I'm going to be travelling to the Central coast of BC in a week amd a half and it will be a nice respite from the heat and probably quite a bit of rain. The 12z gfs has well over an inch of rainfall for the region I'm going to ( Bella Coola) for the few days I'm going to be there and I'm liking it! It seems like the only rain I'm going to see this summer is when I leave the area and go a few hundred miles North.

  18. This is why experience matters!
    Paul Tolleson (NWS Portland) weather discussion:

    The models are making this a challenge to forecast how hot the temperatures will get as some of the raw, "unprocessed" surface temperatures suggest some outlandish values of 110 or more at some locations, which at Portland would shatter the all time record of 107, reached three times, most recently twice in 1981. Looking at return intervals of geopotential heights at various levels such as 500 mb and 700 mb, these suggest that this event is not that uncommon and extreme, though the 850 temps do.

    In my extensive experience at this office, I have noticed the models, particularly the GFS but also the NAM, have had a tendency to forecast excessively warm 850 mb temperatures out 5-7 days that are then lowered some as that time period gets into the day 1-3 period. While we cannot totally discount the model forecasts, for now believe the prudent thing to do is forecast hot, getting close to some all-time records, but not the extreme 110 degree or more values.

    We'll see how it ends up - after all even Mt. Tolleson hasn't seen everything!

  19. NickC - I recall about 10 years ago we actually managed to pull some Gulf of Mexico moisture into Portland! That was a perfect 'storm' of pressure gradients that pulled hard from the southeast, very rare - but a sprawling high over Utah or Colorado can definitely steer the SW monsoon our way.

  20. Granitix - In Portland, 2009 was the last time and it was under similar circumstances.

  21. It's smokey outside today. Hard to even see Tacoma from the Gig Harbor Marina. Mount Rainier is completely in the haze/smoke. It's hot and not clear at all. What's up with that? The smoke I assume mixed with pollutants. Maybe there will be an air quality alert issued soon.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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