June 21, 2021

The Greatest Heat Wave In Northwest History?

Note:  I will update Wednesday morning after the new model runs come out.....


The meteorological community is all abuzz about the forecast this weekend:  several of the global models are predicting an extraordinarily unusual heatwave this weekend in the Pacific Northwest.

A heatwave so extreme that many locations might experience their warmest temperature on record.  

For any day.  For any year.  And doing so in late June, which is not the usual time for the great temperature records.

Waves are the reason for this heatwave

But there is something else...there is great uncertainty in this forecast and what happens will depend on weather events over the western Pacific during the next few days.

Let me show you... the forecasts are simply insane.

To start, here are the forecast temperatures for 5 PM Sunday based on the excellent European Center model.   As high as 121F in the northern Central Valley of California, 113 and 115 in the Columbia Basin, and 104-105 in the Willamette Valley.  Only around 90F near Seattle.


Monday afternoon, Portland is predicted to get to 109F, and 121F is forecast near the Oregon/WA border.


The U.S. model the GFS is also going for extraordinary warmth in the region.  A "plume" forecast plot for Seattle is shown below with the high-resolution prediction (blue line) and an ensemble of many lower-resolution simulations indicated.

For  Monday, the high-resolution run gets to 111F in SEATTLE (the highest on record is 103F); it appears to be an outlier:  most of the ensemble forecasts (gray lines) are cooler, with their mean (black line} only reaching 90F.  


The UW high-resolution forecast system is going for 110F in Seattle and 120F in Portland (see below).  Simply mind-boggling



This is so nuts I can't believe it.

The origin of this potential heatwave is a huge, high amplitude ridge of high pressure aloft  (see the forecast for 11 AM Sunday.   It would represent the strongest ridge in history for our region.


What is the origin of this ridge?  It appears to be forced by a tropical disturbance in the western Pacific that moves northward until it interacts with the jet stream, resulting in a series of downstream waves.  Sort of like deflecting a long rope and having all kinds of waves propagating away.  

The forecast of upper-level flow (around 30,000 ft)  over the Pacific shows the waviness developing (see below).  Think of the lines as pressure and the shading telling you how unusual the winds are.  Wind barbs are also indicated.

On Tuesday morning,  the jet stream is relatively straight over the western Pacific and a weak disturbance is moving northward (indicated by an arrow)



By June 24th, the jet stream has started to buckle, with major waviness over the north Pacific.


And by the 26th, the wave has amplified into a huge ridge over our region


But here is the thing.  These kinds of interactions between a tropical disturbance and the jet stream are very finicky.  Slight changes in the amplitude of the disturbance and where it hits the jet stream can result in major changes in the creation and motion of the jet stream waves.

This produces a great deal of uncertainty.   By Wednesday, it all should settle down and we should have more confidence in the forecast.

My own evaluation from looking at a wide range of forecast guidance is that Seattle northwards will escape the worst of this, with temperatures only rising into the mid-90s, but Portland, the Willamette Valley, and the Columbia Basin will experience historical, extraordinary high temperatures.


40 comments:

  1. I hope the high end temperature forecast is akin to a forecast snowmaggedon that fails to materialize. Temps those high in Seattle could be lethal.

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    1. I hope so too. We simply aren't set up for extremes here, whether they're heat or snow. The elderly, especially, can die in heat like this.

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  2. Oh Lord, I guess we won't be renting the chipper this weekend, my Father's Day present....

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  3. Thank you for a clear and understandable explanation, which is hard to find elsewhere without global warming histrionics thrown in.

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  4. Oof. I remember the 2009 one, 103 was brutal with no AC

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    1. Yep, me too, and I was on vacation when that occurred and in a reinforced concrete apartment, on the top floor, facing west, on Seattle's Capitol Hill no less. :-) No AC then either.

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    2. I sat in my backyard’s fish pond to cool off. 😂

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    3. I sat in my backyard fish pond to cool off. 😂

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  5. Cliff, it's been cooling off at nigh, in the 50s, which has been really nice. It may continue doing so although only into the 60s during the weekend. This has not always been the case in the early summer in Seattle. I remember a few years ago, probably 2014, it was very hot during the day in late June or early July but still in the 70s at night. Is there a reason why this year we are being "blessed" with the cooling off at night?

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  6. I suppose this validates my decision to bite the bullet and install air conditioning a year ago. With AC becoming more common in our area, I wonder if the area's electric grid will be able to handle the surge in demand that would come with temperatures in the upper 90s or higher.

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    1. Imagine when the time comes when everybody is supposed to switch to EVs. Personally, I see no need to install AC. Just keep the fans blowing and let it cool off at night :)

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    2. Pat yourself on the back for that decision!

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  7. Chris B is absolutely correct that temperatures over 100F could be lethal without AC, especially for several days. We need an update, but I'm sure Cliff won't let us down. It's somewhat comforting the ensemble variance is so large. Hopefully the temperatures will fall near the black line, because 90F or even 95F is quite a bit more manageable!

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  8. 90+ is too hot for me. Seattle averages about one day in the 90s each year. The record year being 2015 with 10. Hopefully we don't get into record territory this year.

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    1. I believe the average number of days in the 90's is 3 a year. And, the peak was 12. A number of years have no days in the 90's.

      I agree with the sentiment about avoiding record territory for temperatures. Let other areas have the experience.

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  9. Hottest day in history? Even if it's the hottest in this or that place, we're talking about temp records that don't go much past 150 years.

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    1. And those records are what is known as history:
      : a chronological record of significant events (such as those affecting a nation or institution) often including an explanation of their causes

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    2. Of course they are history, but with such a short record, any "record highs" and "record lows" must include, in some form, a big asterisk.

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    3. You can't have a "Record" high or low, without records. Everything before those records is the asterisk...how far back are you going? I mean, it was exceptionally hot during the years the earth was molten, so...anything after that isn't going to set a record.

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    4. More than 150 years, and less than 4 billion. LOL

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  10. This kind of wobble in the heat stream is predicted by climate change, isn’t it, Cliff?

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    1. No! Climate change does not predict daily weather patterns.

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    2. Hmmm, perhaps it's a trend smart guy?

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  11. I really appreciate weather predictions given in degrees of uncertainty, with ensembles showing the outliers, and not just some "percent chance" single digit.

    And I wish more things in life that we can only model this way were presented to us by major media sources with at least some mention of statistical significance.

    Thank you for the clarity around the uncertainty!

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    1. This!!!!!

      I often think than many if not most of our world's ills are due to mankkind's relentless demands for absolutes, when the answers take chance into consideration and don't submit to binary was of thinking.

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  12. Look at those temperatures on the coast: lows 60s for the most part. Book your hotel room now!!

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    1. already did. This weekend has very, very low tides.

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    2. so did we
      hi 60's to low 70's ocean shores to moclips.
      unfortunately no clamming but what the heck

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  13. It's correct that high temperatures can be lethal, but it's important to say for whom? Mostly the elderly. There is no reason to spread panic. If you are in the at-risk category, there are things you can do, like staying hydrated, avoiding big meals, eating fruits, ... Panicking almost always makes things worse.

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    1. I am one of the mostly the, "elderly". But I happen to have every option. I can eat fruits. And stay hydrated. But there are elderly people without those options. I think panic, for them, is appropriate. What do you even know about what it's like to be elderly, or not have any options?

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    2. Make sure that sodium intake goes along with hydration. Augment your water intake with a small serving bag of pretzels or a sports drink. Bananas are also a plus. Cut back on the caffeine and alcohol. Basically prepare as if you are about to run a marathon, only skip the spaghetti dinner the night before and definitely skip the strategic placement of bandaids

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    3. Unknown, people who are heat sensitive need to stay out of the sun and probably indoors. Cold temps are more hazardous by far, but those who are especially vulnerable to heat need to get a fan. If worse comes to worst, go to a store or a library and hang out. Not rocket science.

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    4. Panic at any age for any reason does no good. Be prepared as best you can, ask for help if you need it and remain calm. Our world is already immersed in an ocean of panic and adding to it for this weather event is helpful to no one.

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    5. Unknown, I remember that this was the advise that was given on TV when I was a child. I think that babies also suffer from the heat. Then it's important that the parents remain calm.

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  14. Thanks for the clear and concise explanation Cliff! I can only imagine the fear mongering taking place over this on the mainstream news channels...

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  15. Thanks for the clarity. I hope that people avoid setting off fireworks. Stupidity could cause a huge nightmare.

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  16. As of this morning (6/23), the Weather Channel is still forecasting 100-103 by the weekend, with 89 on Friday, 100-103 Sat/Sun.

    Will be interesting to see how it all plays out. Currently at 7:27AM, it's cloudy, but only in the mid 50's, with partly cloudy skies and a high of 78.

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    1. The 12Z GFS run from this morning is pretty consistent with its past several runs: https://www.pivotalweather.com/model.php?m=gfs&p=sfct&rh=2021062312&fh=6&r=us_nw&dpdt=&mc=

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  17. My permit to climb Mt. St. Helens is this Sunday. As of now, the forecast for Cougar (300ft asl) is a high of 108. The trailhead should be 10 degrees cooler, yikes. Cliff, do something!

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

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