Last 90 Degree Day Today? Big Changes Ahead

pm Wednesday

It was briefly hot out there this afternoon, with PDX reaching 90+ (91) for the 31st time this summer.

90 Degree Days Summer Heat

Easterly flow topped out between 20-35 mph at the west end of the Gorge this morning.  Pressure gradients turn back to light westerly on Thursday which should keep us below 90 degrees.

Was it the last 90 degree temperature in Portland this year?

It COULD be, especially considering we see no real warm/hot weather in the next 10 days.  That would take us to mid-September.  It’s interesting to note that in the past 6 years we haven’t reached 90 beyond September 20th.  The AVERAGE date for the last 90 is today…the 5th.  So there’s no reason this couldn’t be our last 90 of the season.

Mark Last 90 Degree Day Heatwave

It’s pretty obvious that we’re headed into a cooler pattern after Friday.   The warm upper-level ridge over us

Jet Stream Forecast 2017_1

gives way to a cool upper-level trough much of next week.

Jet Stream Forecast 2017_2

This means much cooler and cloudier weather is on the way; check out the ECMWF ensemble temperature forecast for the next two weeks in Portland.  Pretty good agreement with the operational model here.  Notice it shows coolest temps (relative to average for this time of year) appear to be early next week:


But the million dollar question…HOW MUCH RAIN?

If we’re going to be cool and cloudier, let’s get a good inch or two of rain.  But as of now that doesn’t look likely based on the GFS and ECMWF models

Both show at least 0.25″ in the lowlands, maybe even 0.50″ if we get lucky through next Thursday.  As expected they do hint at heavier rain in the Coast and Cascade Ranges.  Regardless, it’s obvious this will put a big dent in the fire season.  Even a little moisture this time of the year (with its low sun angle) can do a lot of good.  Check out an interesting fuel moisture graph that covers stations on the west side of Mt. Hood National Forest

RAWS_MtHoodWest A “1000 hour fuel” refers to large fuels (8″ diameter or larger).  First look at an “average” year…the gray line.  In the north Cascades of Oregon fuels in a “typical year” are driest just after mid-August and then gradually moisten up through September and October.  The red line is the driest the fuel has ever been (on any one date) through the period of record.The yellow line is last year; see how that dry east wind period around Labor Day kept fire danger extremely high until the 16th of September?  The Eagle Creek Fire blew up during this time and there were other huge fires burning across the Willamette/Umpqua National Forests.  You can see the season-ending rain event the following week as many inches of rain fell in the forest; a somewhat miraculous event for this time of year.  Also note the record minimum fuel moisture was set a few times last year, including much of early September.  This year we seem to have “bottomed-out” around the 20th of August, setting a few new “record dry” days just ahead of that time.  Showers and cool weather moistened things up the last week of August and earlier this week so right now we’re running just slightly drier than average for early September.  Hopefully it all makes sense, of course you can click on the image for a larger view.

To summarize:

  1. We have two more warm days and then we see a sustained period of cooler than average temps.
  2. Put anything away that can’t get rain on it Friday, or for sure Sunday
  3. If you have an above-ground pool like me, it’s likely it’ll be too cool to use after Friday.
  4. Fire Season 2018 should quiet way down next week, maybe not the end of the season but we will have passed beyond the threat for major fires.

Chief Meteorologist Mark Nelsen



37 Responses to Last 90 Degree Day Today? Big Changes Ahead

  1. K says:

    Another boring fall and winter ahead, I guess. Sigh.

    I’m getting really bummed out by all this boring weather.

  2. Matthew says:

    I just wanted to complain about the new forecast graphics the website is using. I really hate them. It’s harder to get a feeling for the weather during the week. I miss the more artistic look…..

  3. Roland Derksen says:

    A few light showers early yesterday evening, and a few more this morning, and that’s been it- so far. Apparently, overnight and tomorrow is when the rain is really coming in: Could get over an inch in 24 hours if the forecast is true.

  4. Ken in Wood Village says:

    I’m surprised no one has said anything about the 12Z EURO. I will say this, I really like it a lot. If we go by the 12Z EURO, we will have a good wet week and by next weekend we could see a good Low come in. 🙂

    • Joshua Lake Oswego says:

      00z GFS hugely backed off on the rain for next week and warmed us up. Betcha the 00z ECMWF will follow. Low will be too far offshore as always. Glancing blow instead of a direct hit. My prediction is for .08” at PDX for Monday-Sunday.

      • Ken in Wood Village says:

        Joshua, your such a buzz kill…lol. I always thought the EURO was the model to always look at and not the GFS!! We’ll see what the next couple of runs for the EURO will say. I’m thinking (hoping) the EURO is the leader instead of the GFS. 🙂

        • Joshua Lake Oswego says:

          I know, I know. I can’t help it. I know how this story ends though. Fool me once… Fool me 6 times… Look at the 12z suite. Bye bye anything more than scattered showers for a few days.

  5. Jason Hougak says:

    You all with city water your using for the yard should drill a well if possible. I’ve done a few right in town if the yard has enough room for the drilling rig. We did one right in Milwaukee area by the Willamette River by Elk Island.

    • W7ENK says:

      The City of Milwaukie doesn’t allow you to drill your own well. If you pull yourself off their municipal water supply, they’ll condemn your property for code violation. The only exception to that is for properties that had their own wells before that mandate went into effect. The property you worked on was either just outside of Milwaukie city limits, or already had an existing well that was grandfathered.

      And get this: My property (house built 1921) used to have a well, but it was decommissioned some decades ago. I’m not allowed to reopen that well, nor am I allowed to drill a new one. The exemption does not apply because the house has been connected to the municipal supply. On top of that, all of my storm water gets piped into a 400 gallon underground cistern, none of it leaves the property, and it’s been that way since the house was built. I don’t even have any lines running storm water into the drain that dumps into the sewer, and yet I’m still charged for storm water. I’ve also challenged that with the City (short of hiring a lawyer and taking the matter before a judge) and they insist there’s nothing they can do, and I still must pay the fee.

      At risk of violating Mark’s Rule #1 (No politics) and triggering another one of Kyle’s random, mostly nonsensical tirades, I’ll say this: Like most everything else in government, it’s a total racket.

  6. Tim flynn says:

    Winter Forecast

  7. Ken in Wood Village says:

    There was 2 lightning bolts in the coast range 😮🤔😏

  8. Paul D says:

    The 7-day forecast currently shows that it will be 68 and scattered showers today.

    What is going on?!?!?

    • Paul D says:

      Now it shows 72 and scattered showers for Friday (today)! Why does it even show today when it’s almost 7pm? The old 7-day forecast never used to do that.

  9. W7ENK says:

    Free sky water is welcome. This has been an expensive Summer!

    • Ken in Wood Village says:

      I hear you there. Our PGE bill has been sky high. I take care of my mom, and with the warm to hot temps, have been a challenge to keep the condo cool enough so she doesn’t get to hot. I’ll be glad to had fall like temps and hopefully rain 🙂

    • Joshua Lake Oswego says:

      I hope we get at least .25”. I’m not feeling too confident of that though. There has been an advertisement of a good soaking so many times in the last few months only to have it fizzle out and we end up with a couple hundredths of an inch or a trace. We need a widespread soaking. These relatively weak unorganized showery systems break apart or get absorbed by the coast range. Or, they are too hit and miss to be meaningful.

    • Paul D says:

      I just had my most expensive water bill ever! Not fun 😦

  10. JohnD says:

    In a lot of years, September is one of the nicest months of the entire year around here–all things considered. We’ll see how the remainder of this one plays…

  11. WEATHERDAN says:

    IT people always seem to want to redesign web pages that work and look just fine. My guess the reason for that is so the rest of us won’t notice or complain how over paid they are. Peace.

    • Anonymous says:

      I respectfully disagree, I think the IT team has done a very nice job. I can finally use KPTV on mobile when before it was unusable on my mobile browser. The site is exponentially quicker than ever before. Keep up the good work IT guys!

    • Paul D says:

      If it ain’t broke, don’t fix it. They just don’t listen….

  12. Roland Derksen says:

    Intresting to note that Oct.5,1980 was the latest recorded 90 degree day in Portland. For me, that was my latest 80 degree day.

  13. Paul D says:

    Those 80+ temperatures just won’t go away. They’re now into Friday and the chance of rain is gone.

    I’ll believe we’re done with 90+ temps when October hits. This is the year of the early and l-o-n-g summer 😦

    • K says:

      The chance of rain isn’t gone, next week looks showery and models seem to be continuing to push the jetstream south allowing for stormier weather. I don’t believe this week was supposed to offer any rain chances.

      • Ken in Wood Village says:

        I agree K. How have you been? What I have been seeing in the models for the past week is the fact the High gets moved West and we finally get a NW flow. The Euro seems to want to bring disturbances down in the NW flow. Maybe this is the start of fall!!! It would be nice to finally have cooler days and some rain to put out these fires.

        • K says:

          I’ve been great Ken, hope you’ve been well. I really hope we get some stormy weather. Honestly, I wouldn’t mind something like October 13th-15th, 2016, if you remember that series of storms. Really hope something puts an end to this fire season.

        • Ken in Wood Village says:

          Yea, those days were good. I don’t remember the date because I was a kid. I remember being over at my dad’s and we were going to go to the Coast to go hunting. I woke up to my dad and step-mom walking around in the dark. Yea, the power went out. A huge storm was hitting the PNW with winds I think in the 50+mph in the Portland area. We still went to the coast range to hunt (I actually didn’t hunt, my dad and uncle did the hunting) and we went onto a ridge and it was so gusty, the truck would move side to side. It was really intense. I loved it.

          It’s amazing when your a weather geek and you remember the worst storms to hit were you live…lol. That tells you how much you love the weather. 🙂

    • Roland Derksen says:

      We’re back to the heat (82F) and smoke here this afternoon.(Groan). Can hardly wait for the showers to get here tomorrow. I wish they would travel down toward you as well.

  14. Ken in Wood Village says:

    Thank you Mark for the detail on what’s coming up. I thought the same thing when looking at the model runs.

    I do have a question Mark, what’s up with the Weather Page on The weather blog isn’t on that page? Will the IT people be fixing it??


    • Paul D says:

      The whole KPTV web site is redesigned, and it ain’t pretty. The 7-day forecast is pathetic.

      • Ken in Wood Village says:

        Yea, I sent Mark a email earlier today and just received a email back. Mark says, “it’s a mess, but a work in progress” LMAO. Just wish the IT people would have gotten it right the first time…lol.

        • Mike says:

          Yes, I wish they would leave things as they are. I have very much enjoyed the way its been for a lot of years.

        • Matthew says:

          I just wanted to complain about the new forecast graphics the website is using. I really hate them. It’s harder to get a feeling for the weather during the week. I miss the more artistic

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