An Early Fall “Heat Wave”

We’re all set for some hot weather this week.  The stage is set with:

  1. A strong ridge of high pressure in the upper atmosphere developing overhead.
  2. A “thermal trough” of lower pressure develops over the Coast Range/Valleys Tuesday afternoon through Wednesday evening
  3. Offshore (easterly) wind flow shows up due to this Tuesday afternoon and continues through late Wednesday
  4. No clouds to obscure the sun

How warm?  850mb temps peak out around +21 to +23 from Tuesday-Thursday afternoon.  According to my September chart, that puts us in the 91-95 degree range.  However the offshore flow is only for Tuesday and Wednesday.  In early-mid September, as soon as we lose the offshore flow it’ll be hard to get temps to/above that 90 degree mark.   Record high temps for Tuesday-Thursday in Portland are 98-94-92.  As a result I think Wednesday gives us the best chance of tying or breaking a record high.

How about those nights?  Yuck…unusually warm again since we have relatively high dewpoints (for September).  Record warm lows the next 4 days are 63-61-60-64.  We should be quite close to those records.

Check out Brookings today, a high temp of 101 after a low of 80!


How’s that for offshore flow?  It’s a classic case of the Brookings Effect (also known as Chetco Effect).  I’ll let Wikipedia do the work of explaining it since it appears to be a reasonable explanation.

Let’s move on…quite a change in the 2nd half of the 7 Day forecast the past few days.  Just two days ago it appeared that we would see a rapid cool down Friday and beyond.  Instead it now appears some ridging holds on through at least Saturday, possibly Sunday.  As of this afternoon the ECMWF is bringing a chilly trough through quickly Sunday and Monday.  I totally ignored that while making today’s 7 Day forecast for one reason, that ECMWF operational run was a complete outlier compared to ensemble members for Thursday-Friday.  See how the blue line on the chart below is far below just about all the others?


The GFS is much slower with the cool down…see its chart.  But also notice it’s a little on the warm side for the early part of the weekend.  Due to this, I didn’t ramp temperatues back up Saturday/Sunday (90+) as the 12z/18z GFS would suggest.


Big picture…unusually warm and sunny weather will continue through the first half of September.  There ARE signs of a significant cooldown for next week though, see the below average temps on the charts above, plus here are 4 weeks of ECMWF average 500 mb height maps.  These are from last night’s run:





Chief Meteorologist Mark Nelsen

38 Responses to An Early Fall “Heat Wave”

  1. I see the NWS is hinting at some T storms again. That’s fine, but I don’t need another 3″ of rain in one fell swoop like last week’s storm.

  2. WEATHERDAN says:

    Salem had a low of 62 this morning. We are approaching 30 nights of 60 or more for the Summer. This is a record for us. The previous record was just 21 nights in 2007. Our average is 11 nights per Summer. As recently as the 1970,s we averaged 1 such night each Summer. This is concerning to me. Our dewpoints also have been incredibly high this Summer. Many days this Summer our dewpoints have been in the 60-65 degree range. Here it is in mid September when we should be seeing quite a few nights in the 40,s instead we are still seeing high dewpoints and lows in the 60,s. Our daytime temps have gone up a bit over the last 50 years, but our nights have really gotten warmer. Peace.

  3. pappoose in scappoose says:

    Greater Portland Metro Area
    Special Statement
    Statement as of 6:08 AM PDT on September 10, 2013

    Temperatures at the lower elevations inland today will likely
    reach 90 degrees at many locations… and perhaps even reach into
    the lower 90s. Temperatures inland on Wednesday are expected to
    reach the mid 90s at many locations. Record high temperatures
    today are in the upper 90s at most of the larger cities… but only
    in the mid 90s on Wednesday and could be reached.
    Be sure to drink plenty of clear liquids today and Wednesday.

    Drink plenty of clear liquids today…Hahaah!

  4. archangelmichael2 says:

    To make this brief. Does anybody feel as if with all this warmth like Weather Dan said we haven’t experienced since 1967 we are on borrowed time for a period of below normal night time temperatures?

    Early freezes?

    • paulbeugene says:

      In Eugene: 1990 and 1992 had warmer summers than what we had in 2013. Law of averages suggests what comes up comes down.

      16 days after all time September record high in Eugene of 103F in 1988, record low of 34F set.

      16 days after record high of 96F set on 9/12/99, all time (for airport location) Sept low of 31F set.

      I’m not suggesting record low will be set on Sept 26 this year but it should be cooler next week.

      Ski season still three months away, give or take a week or two.

  5. schmit44 says:

    9/9/2013 Oregon (All) Temperature Summary

    High:101 at Brookings (US 10( 150 ft) & Brookings Airpor(459 ft)
    Low: 80 at Brookings Airpor(459 ft)

    High:56 at HOWARD Mt Howard(8150 ft)
    Low: 29 at DW9636 La Pine (4236 ft ) & KIRK (4519 ft )

    Largest Diurnal Change: 53 degrees
    Beatty (86/33 ) (4320 ft )
    KLAMATH NWR (83/30) (4531 ft)
    Sand Creek (US 9 (83/30) (4525 ft)
    DW9636 La Pine (82/29) (4236 ft)

  6. Sifton says:

    I’ve often said & pondered about a “winter home” in Brookings!! 1 of these days………(or years for sure!)

    • dharmabum says:

      Ditto for us too! We are in fact going down there to scout it out in early October for a possible permanent residence, I could dig the possibility of the chance of an 80 degree day here and there during the winter.

  7. Dewpoint back up to 60 degrees at DLS = absolutely disgusting in September! Interesting from a geek perspective, but disgusting to have to live through.

    Also…is that an early October “Indian Summer” ridge trying to show up on week 4 of the ECMWF anomaly maps?

  8. Nice weather today, not looking forward to mid 90’s Wednesday though.

    • High Desert Mat says:

      In September mid 90’s are short-lived in the afternoon. Its more of a spike than 80’s in late morning and late evening. It heats quickly and cools quicker. Just sayin

    • Paul D says:

      Agreed! 90’s totally suck. Looking for some 70’s!

    • W7ENK says:

      Just be patient, your 70s are coming. FWIW, it should be in the 70s here shortly, and between 8 and 11pm this evening, then again between 10am and about Noon tomorrow. Same for Thursday and maybe Friday. There’s your window of opportunity this week, so get out there and enjoy those 70s!


  9. archangelmichael2 says:

    I got 2.8 out of the rain gauge despite the dome holding off the worst of the lightning though several flashes were really loud.

    I counted about 40 lightning strikes and loud rumbles while it seems Salem and places south had up to 300 in various areas! 😮

    The dome almost took over but the monsoon rainfall killed it! 🙂 It’s amazing that now there is absolutely no traces whatsoever of that rainfall.

  10. W7ENK says:

    Interesting, how we’re bookending this summer with an early season hot spell and a late season hot spell with not a whole lot of anything remarkable in between. Kinda reminds me of the winter of 2010/2011, with an arctic cold snap in November and another in late February, but a whole lotta nothing in between.

    Just an observation, not saying that means anything… likely, it doesn’t.

  11. Jesse-Stevenson says:

    Mark, could you link me to that EURO ensemble chart?

  12. BoringOregon says:

    1st !!!!

  13. Lynn says:

    Please tell me this will be it for the heat.

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