Heat Wave This Weekend

8pm Thursday…

We are entering the final stretch of Summer 2020. Just a little over two weeks left in August. So far this summer has been near normal temperature-wise. Notice no real anomaly (much warmer or cooler than average) since mid-May

Of course the first half of June was very wet, but since that time it’s been VERY dry. PDX has only seen 0.26″ rain in the past 8 weeks! But that’s not unusual and I sure don’t see any sort of real rain in the next 10 days.

We do have at least a four day heat wave on tap.


  1. Expect hot weather Saturday through Tuesday. The first two days will feature high temperatures somewhere between 98-102 degrees in the western valleys of Oregon and extreme SW Washington
  2. Next week looks warm/hot even after we get a “cool down” Monday.
  3. Very warm temps make it to the ocean beaches Saturday and at least part of Sunday.
  4. There’s no sign of thunderstorms west of the Cascades through this stretch
  5. By early next week we will have reached our yearly “allotment” of 90 degree days. That’s 13 days, but about to become 14-15 when new climate normals come out next year. For the 2011-2020 period, we’ve averaged 17 per year! This year we’ve seen one in May, June, six in July, and one in August (so far)

Weather Geek Talk

A strong ridge of high pressure has begun developing over the Western USA. By Sunday/Monday it looks about like this around 18,000′

Models have been trending with a stronger ridge and hotter atmosphere overhead this weekend and beyond. Today there is excellent agreement that over Salem we’ll see 850mb (C) temps jump to +19 tomorrow, +25-26 Saturday PM, +22-24 Sunday PM, then down to +18-20 Monday/Tuesday. I just checked my “August Chart” for 850mb temps. In the 10 year period from 1999-2009, the highest afternoon temp in August was 24.5 degrees. Folks, this is a “top tier” heat event coming up!

Alright, so what about surface wind direction? That becomes very critical from mid-August into fall. No offshore flow and we’re not going to hit 100 degrees. Tomorrow the pressure gradient goes flat across the Cascades/Gorge. No windsurfing at Hood River and calm conditions for that fire out in Mosier. But a “thermal trough” develops along the coastline tomorrow night and Saturday. Here’s a classic sea level pressure map for a heat wave; click for a closer view. Saturday at 5pm

I see 3-4 millibars easterly flow through the Gorge Saturday. Add in the crazy hot atmosphere overhead + all sunshine = we’re headed to/above 100 degrees. In theory we could be as high as 104, but I decided to go with a 102 Saturday, assuming easterly flow won’t be TOO strong. That’s after checking the 2008 and 2016 heat waves that produced 100+ temps in mid-August. You can check out blog posts from each of those events (lower right side of this page). Maybe most interesting is that there’s no reason to panic if it’s only 80-82 at noon Saturday; we can easily jump 20 degrees after noon in this pattern.

Saturday night should be a VERY warm night; possibly only dropping to around 70 well after midnight in the city. Easterly flow goes away Sunday, but with such a warm start + hot atmosphere we should still hit 100 in the afternoon. Of course if we have any significant high cloud cover (some models show that), we won’t hit 100. Here’s 2pm Sunday as the thermal trough is about to push east of the Cascades

Finally, a strong push of marine air should drop us 5-10 degrees Monday; “only” a high around 90 or so. But notice this chart shows 850mb temps (from ECMWF model) remaining above average through most of the next two weeks. Green is the average temp (notice it goes downhill in late August), blue is average of all 51 ensemble members. Each thin line is one ensemble member

Enjoy the cool temps tonight, and try to stay cool this weekend. Here’s our ocean beaches forecast; the left side forecast temp for each day is the central Oregon coast. Right side is up on the north coastline, including Long Beach peninsula. In general it’ll be quite a bit warmer the next few days up around Cannon Beach and Seaside

I’ll be on vacation tomorrow through most of next week so probably no posts until Saturday the 22nd.

Chief Meteorologist Mark Nelsen

60 Responses to Heat Wave This Weekend

  1. Joshua Lake Oswego says:

    I’m close to the Rivergrove area of Lake Oswego. Far SW LO.

    Look at reporting stations on Ambient Weather or Weather Underground. You are at the high end for all of the metro area. Most are well under .05”.

    • W7ENK says:

      That’s very strange. NWS officially tells a completely different story, especially to the N and E side of the forecast area.

      I ended Friday with 0.22″ after several hours of moderate to heavy rainfall that began around 8pm. It was still raining lightly at midnight when I dumped my rain gauge. Got another 0.02″ after going to bed, which went on Saturday’s record. It was a good soaking, the streets were still wet in the morning when I got up, and there are still a few (shrinking) puddles left on my street.

    • W7ENK says:

      Rivergrove is pretty much exactly 7.0 miles to my SW as the rain cloud flies. It also places you in upslope terrain on the front side of the West Hills for weather coming out of the SW, which should provide a bit of orographic lift right over you. It also places me in your rain shadow.

      I also think your anti-rain bias might have misled you by an entire order of magnitude. Friday’s official NWS reading at PDX was 0.20″, not 0.02″, FWIW.

  2. Joshua Lake Oswego says:

    14 nights with lows in the 60s so far in August. Gross. Looks like we get some lower dew points with lower over night temps next week.

    • Kyle says:

      This weather is literally poetic justice for all you Washington/Portland fans making fun of us for saying it has been warmer down here.

      We have had more stretches of 90F weather down here then up there! We are at like day 15 or something but now it’s more humid up down here and up north! 🤣

  3. Joshua Lake Oswego says:

    We’ll be lucky to get .05”. Whatever we get should be wrapped up before noon. The Olympic peninsula and parts of BC are going to get soaked. I’m jealous.

    • W7ENK says:

      So, this morning’s AFD and reality both say otherwise. It’s been raining (more of a heavy drizzle) across the river from you off and on since 4am, and continuously now for over an hour. Already 0.08″ in my gauge, and the real rain isn’t even supposed to start for another few hours, lasting into this evening.

    • Joshua Lake Oswego says:

      Officially, .01” so far today. Same with at my house. I’m not wrong yet.

    • W7ENK says:

      Not really sure how, considering we’re less than 4 miles apart (as the rain cloud flies), you’re more or less upstream from me, and I’m at 0.09″ as of 10am, which is roughly when it stopped raining. Evaporation, maybe?

      More on the way this afternoon/evening…

    • Roland Derksen says:

      Yes, some places around here are reporting getting soaked- although I can’t say it’s been all that much yet around my location. But it’s early in the afternoon, so we’ll have to see how it goes.

  4. Paul D says:

    What’s the timing of the rain look like for Friday? Hopefully not in the morning – I’ve got some concrete to pour!

  5. Roland Derksen says:

    Some light rain periods overnight here- not too much in amount yet, but more is coming today and tomorrow. One thing about this August- we’re likely to have above average rainfall despite the sunshine and heat.

  6. W7ENK says:

    It was supposed to be cooler today than yesterday. It was 96 degrees today in North Milwaukie. Yesterday, it was 97. So by Mark’s standard, does that mean that today was, in fact, NOT cooler than today?

    Maybe the humidity… nope, never mind. Today was also muggy AF. 🤷🏼‍♂️

  7. Roland Derksen says:

    We had a high of 93.7F yesterday. That’s my highest temperature since August 2016- and it sure felt like it. Last night was interesting; Some clouds moved over and produced a few light thundershowers. I only had a trace amount here, but further up the coast apparently there was a real thunderstorm.

  8. JERAT416 says:

    Bust, because of clouds?

  9. Pat says:

    94 degrees and drizzle in Portland as of 4pm, according to one official weather site, interesting combo, should make for an interesting evening. Also, if this cloud cover holds, tonight might be warmer than last night.

  10. JohnD says:

    Took my Grandbaby for a walk an hour ago. Came back drenched. Super hot/humid. Rare for us to have a summer day like this—more like East Coast weather. Maybe the equivalent of rare cold/snow event day in winter!

  11. Andy says:

    Good shower went through Albany…looking better on Radar.

  12. W7ENK says:

    96 degrees and humid AF, with a slug of moisture moving up from the South…

    • Ken in Wood Village says:

      It’s looking good for a chance of thunderstorms. Just looking at the radar, things are starting to get active 😉

  13. Andy says:

    Looks like some showers south of Albany moving north. no lightning on radar though…hoping things build up stronger, but the overcast may cap things off with the heating.

  14. Joshua Lake Oswego says:

    Running +3.5 degrees compared to yesterday at this time… 85.1. Identical humidity.

  15. Paul D says:

    Today’s high has been lowered to 98 @ PDX. I feel so much better 🙂

    • Ken in Wood Village says:

      The Humidity is what’s going to hurt today…lol. I’m seeing the chance of thunderstorms (probably closer to the Cascades tho). You should start seeing higher clouds in a couple of hours. I do see a couple of showers around Eugene and moving North. I would keep an eye to the sky 🙂

  16. Ken in Wood Village says:

    Things are changing a little fast for today. It looks like we most likely won’t see 100 today. Another thing we could see today would be thunderstorms.

    I see there was a shower that came through an hour or so ago. It’s up past Mt. St. Helens now. I do see more showers NW of Medford but more closer to Tri-City, Oregon. These showers are moving really fast (at least what I see on the radar). I looked at the Satellite picture, There is a lot of moisture in the lower levels going all the way up to the Upper Tropospheric area. Even if we don’t hit 100, it’s going to feel much warmer with all the Humidity in the air. Right now, Troutdale is at 65% humidity.

    I’m keeping an eye on the weather today, I think you may want to too.

  17. runrain says:

    Happy Valley 6:00am…

    74 degrees…

    Big, fat raindrops for 2 minutes…

    Was this on your 2020 bingo card?

    • runrain says:


      Severe thunderstorms this morning in San Francisco…

      Lightning-caused fires in Marin County…

      And the tornado northwest of Reno yesterday created by the Loyalton Fire pyrocumulus cloud…

    • Ken in Wood Village says:

      I just posted something about what I believe could happen today. I was wondering, were do you live again?

  18. Paul D says:

    Should we call a forecast bust? It only hit 99 @ PDX.

    • Tanis Leach says:

      The rule of thumb Mark has is if it is within 3 degrees of the forcast high, it is considered accurate. Personally I rank it as:

      Spot on or 1 degree off: 100%
      2-3 degrees off: 70%
      4-5 degrees off: 30%
      6+ degrees off: nothing.

  19. W7ENK says:

    And it’s supposed to be even hotter tomorrow?

    JFC, this is pushing my limits… 🥵

  20. Evan -- Cedar Mill says:


  21. runrain says:

    Extreme fire behavior of the Loyalton Fire northwest of Reno has generated a tornado warning! Never seen that before.

  22. runrain says:

    Slight chance of thunderstorms west of the Cascades Sunday evening.

  23. boydo3 says:

    Not missing those 95-100 deg summer highs. Down here on the south coast it was another pleasant summer day with a high temp. of 80 at my location.

  24. Roland Derksen says:

    I may have to raise my prediction for the temperature on Sunday here: 88F seems too cool now. Probably at least 90- depends on what the wind does.

  25. oldwxwatcher says:

    What a bad time for my heat pump to be on the fritz. 😦

  26. Kyle says:

    I bet if we add Oregon to the list of if the PNW is getting hotter instead of just looking at WA and BC it would paint a VERY different picture!!! 🤣.

    A lot of people’s biases would be shattered.

    We are a mini Sacramento now.

    • W7ENK says:

      Oregon already is counted as part of the PNW tally, WTaF are you talking about, Kyle?

    • Roland Derksen says:

      Kyle, it gets hot in southern BC too- maybe not often here by the coast, but inland (eastern Fraser valley and Okanagan valley). Do you know we actually have a desert north of the border at Osoyoos? Cacti and sagebrush grow there.

      • W7ENK says:

        Kyle doesn’t particularly like facts. They tend to scare him and send his schizophrenia into a frenzy. 🤷🏼‍♂️

  27. W7ENK says:

    The first sentence of this post is an incredibly painful dose of reality. Having been cooped up at home for 5 months now, I’ve had no choice but to watch the seasons whizz by outside my windows. At the start of all this, the trees were still completely devoid of any foliage. It seems like Summer just got started, and already we’re sounding its death knells? Before I know it, there’ll be snow falling out my windows, and I’ll have no excuse to go play in it. The old “Oh, sorry boss, I can’t get my car out of my driveway!” excuse doesn’t work anymore, when one works from their guest-bedroom-turned-home-office all the time. I guess I’ll just have to work on my “kehhek-kehhek… I don’t feel so well today” voice. 🤷🏼‍♂️

    All that aside, the weather over the next several days looks HOT! And I love it!! Especially since it’s only a couple of days each year (100+), and that’s if we’re lucky. Much like our snow events, really.

    Had what will probably end up being my last fire of the Summer this evening. Probably won’t be able to do this again until October.

    Stay cool, folks.

  28. Paul D says:

    Aha! So we have had nine 90+ days so far!

    This weekend is going to suck! Way too hot.

    • Kyle says:

      Next 100 years are going to be a lot worse until it cools again! However the shining silver of hope is the GSM we are in with the sun! Though it doesn’t seem to be having much of an effect and is it over already?

      In fact be glad we’re not in the 1,000 AD ‘Globular Warming’ Era. It was 2 to 3C warmer then now worldwide.

      Grapes were grown in parts of Canada that are laughable today and when the world abruptly cooled they abandoned it and the farms in Greenland froze over.

    • Kyle says:

      I wonder if this heatwave has a chance of rivaling the famous 1981 one? I told you last month we haven’t seen the end of it!!! .🤣🤣.

      Mother Nature woke up to the 21st century once again!

      Plus there are other external factors far too complex for your minds to handle.

  29. Ken in Wood Village says:

    I wish we could see thunderstorms to cool us off during the night 😢

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