September Looking Like July

July felt like September at times, and now it’s payback time…

Our models have been very consistent the past few days showing the largest weather pattern change we’ve seen in 7 months.  As mentioned NUMEROUS times since March or so, the West Coast has been dominated by some sort of cool upper-level troughing.  During the last half of August this trough has mostly disappeared (not counting this first 3 days of this work week of course).  That allowed temperatures to average out to “normal” for this month for the first time since January.  But now it appears a strong upper-level ridge will build over us and stick around for quite a while.  Most impressive is that all models have the same pattern change, so we have quite high confidence in the big change.

The obvious question would be “didn’t we have major pattern change give us 96 degrees about two weeks ago?“.  We almost did, but the ridging was a bit to our east, and notice the real hot weather only lasted a couple of days at most.  So then the next question might be “just how hot is it going to get?“.  The short answer is that it probably won’t get much above 90 degrees in the next 6-7 days; partially due to the much longer nights and lower sun angle in early September compared to July and the first half of August.  And 90 degrees in September sure doesn’t feel like 90 in midsummer.  That’s due to that lower sun angle and long nights as well.  Temperatures rise and fall quickly in early Fall plus nights are significantly cooler as well.  I should point out we expect it to be very dry (low relative humidity) during this warm spell.

Some models are showing an even warmer pattern that would push us up into record warm territory next Wednesday or Thursday, but that’s a ways off.

The main point is that we have an extended period of very warm or hot September weather on tap, probably 7 days or more.  That includes a cloudless Labor Day Weekend in just about the entire Pacific Northwest.  There may be some low clouds at the ocean beaches by Monday, otherwise cloudless and warm there Saturday and Sunday too.

Chief Meteorologist Mark Nelsen

168 Responses to September Looking Like July

  1. Yevpolo1990 says:

    This is going to fun, a very big cool down is about to happen here in Oklahoma.

    A strong cold front is continuing its southward motion this morning. Very strong north winds… along with much cooler temperatures and a chance of rain or storms… will be associated with the frontal passage. Isolated to scattered showers and thunderstorms may develop by mid afternoon. Isolated large hail and damaging wind gusts may occur. At 1215 PM… the cold front was located from near Beaver Oklahoma to around Pratt Kansas. The front may slow a little during the heat of the afternoon. The front is expected to reach a line from Arnett… to Woodward and Freedom by around 4 PM. Wind speeds behind the front are expected to be between 20 and 25 mph with higher gusts.

  2. bgb41 says:

    12Z GFS @ KTTD

  3. Chuck on Mt Scott says:

    Winds are blowing hard up here since last night. Hope no fires are started during this event. It would get ugly quick.

  4. CorbettTez says:

    Why is there not one mention of East wind on any of the forecasts!? How about a little love and heads up for your neighbors out here and let us know that although it will be warm, we’ll be dealing with 15-27mph wind gusts!? A little time to get some prep work done in the garden would be nice instead of finding tomato plants blown over and debris all over the place! So much for the “great” weekend!!!

  5. bgb41 says:

    Mark pulled the 97 off for friday.. Now maxing out at only 95 thursday on the 7-day

  6. pappoose in scappoose says:

    OK, bring in a good supply of the beverage of your choice, the furnace has been turned on. How about some chilled Horilka, Yev? Hahaah!

    National Weather Service Portland or
    845 am PDT Sat Sep 3 2011

    we may see some lower 90s as early
    as today…even for some of the spots that started off in the lower
    Latest runs of the GFS/European model (ecmwf) show an
    extended period of 90s for the inland valleys…possibly lasting the
    entire week.

  7. Andrew (West Hills) says:

    Going to be a great day today, upper 80’s look likely.

    GO DUCKS!!

  8. As of 7 AM it is 45 here with no wind.

    Meanwhile at Larch Mountain it is 69 with an east wind gusting to 44 mph.

    • DELXV says:

      Looks like Extreme fire weather has started at that location this morning .and it will probably spread.

  9. bgb41 says:

    9/2/2011 Oregon (All) Temperature Summary

    High:98 at BROOKINGS( 79 ft)
    Low: 76 at Brookings Airpor(459 ft)

    High:52 at MT. HOWARD(7910 ft)
    Low: 25 at Mazama (4590 ft ) & CRANE PRAIRIE (5500 ft )

    Largest Diurnal Change: 56 degrees
    Beatty (82/26 ) (4320 ft )
    KLAMATH NWR (82/26) (4531 ft)

  10. It is going to be so hot next week the *brief* “cool down” we do receive Monday and Tuesday down to the 86-89 range(If we’re lucky I’m not sold on it) is going to feel COLD compared to the 92-99 degrees Wednesday through next Sunday.

  11. 00z GFS is……………
    *Drum roll*

  12. rianmuleback says:

    Anyone have any web cams for New Orleans?

  13. 18z is nasty hot next week…. Record breaking heat wave if verified.

    In other news the OTH-GEG Cross Cascade gradient(As seen below) is about to switch to offshore flow. Currently it is +0.2mb. Typically once it is about -4mb we will begin to see the easterlies develop along the ridge tops, Cascade passes, and Foothill locations.

    • Andrew Johnson says:

      It will be interesting to see if I get any easterly winds at my new location. So far I have noticed that my location is pretty exposed to NW and N winds because of the topography, and I would suspect W winds as well. Because of a small hill behind my property I seem to be pretty sheltered from S winds. Not sure about E winds, I think I may be sheltered from them a bit by the local terrain as well.

    • Punxsutawney aka HIOPHIL says:


      Two 100 degree days with two 96 degree days on either side. That would be very respectable for mid July. I haven’t looked at the records, but that could potentially be four record days in a row.

      Hey I thought someone said we couldn’t get an extended heat wave at this time of year. 😉

    • Boydo3 N. Albany 500' says:

      The nice thing about hot weather this time of year is how quickly it peaks and then declines. The not-so-nice thing is how the low sun angle makes it feel like a slap in the face!

  14. Runrain says:

    Only 78 tomorrow, based on the 7 day forecast. Unless the numbers are off by a day.

  15. pappoose in scappoose says:

    Hope the reporters have dug out their chest waders and loaded up the dinghys. Lee is probably gonna float someone around. Hahaah!

  16. WEATHERDAN says:

    My forecast for Salem for Saturday Sept 3rd thru Fri Sept 9th. Sunny every day. Sat 93/53 Sun 97/56 Mon 92/55 Tue 94/57 Wed 98/58 Thur 95/59 Fri 94/56. That would give us 14 days over 90 for the summer. Just about normal. With this pattern looking very warm until mid to late September another 14 days over 80 the rest of this summer looks reasonable. That would give us 55 for the summer. Just slightly below average. So much for that worst summer ever cry that was posted on this blog in June. Sometimes you just have to wait until November to see how it all turned out.

  17. Runrain says:

    Don’t you have to have an overnight freeze before you can have an official indian summer? And is this phrase even allowed anymore? If it needs to be changed, anyone have any ideas? How about Retro Summer. Or Summer Rewind. Or De Je Vu Summer.

  18. It appears the heat wave breaks next Sunday or Monday according to the GFS/EURO.. Seems to be good agreement on this. Whether or not a ULL provides a t-storm outbreak during this is unclear.

    Tomorrow night could be one of those rare nights where the east winds persist east of I-205 with perhaps lows in the 70’s. I remember several years ago it was 81.3 for my low temp due to hot, gusty east winds.

    • 12z WRF-GFS shows a lot of gusty to strong east winds throughout the run especially this weekend and then next week Wednesday through Saturday. This is going to be one heck of a sharp/strong thermal trough.

    • Punxsutawney (aka HIOPHIL) at work by Sunset High elev ~280' says:

      I was thinking we would have that posibility with this pattern and I remember that situation.

      Sometime in the last couple of years I remember leaving Hillsboro on bike and heading east. It was dead still at my place and in the low 50’s. Just east of 185th (3 miles east or so) the east wind was blowing and it was in the mid 60’s. It felt like someone turned the furnace on.

    • Joshua in Lake Oswego says:

      Sounds like my worst nightmare. Hot days are one thing, but hot nights… gross!!!

    • Mark Nelsen says:

      Yep, places like Mt. Scott, top of West Hills, Corbett and Prune Hill may stay around 70 tomorrow night. I loved that when I lived in a windier spot because it was exactly the same as a night in the Hawaiian Islands. Not hot because it was breezy. 70-75 in a breeze after dark is actually a bit chilly.

    • Boydo3 N. Albany 500' says:

      Ahh…those tropical breezes, lapping surf, rustling palm trees….

  19. bgb41 says:


    Come join this friendly discussion on facebook. Currently 80 people are in this group. With the big heatwave coming, now is a great time to come join.

  20. Jbpdx says:

    Way too many lingering ugly gray clouds this morning in Hillsboro. Hope it’s the last I see for weeks. Yesterday started out perfect—clear and azure.

    By the way, whoever determined that a sky totally covered in thin clouds is considered “clear” or “fair”? I think not.

  21. Well 6z did seem to offer a glimmer of hope for a bit less heat and shorter in duration, but 12z has other ideas…. Looks unpleasantly hot. Quite a bit more offshore flow advertised as well.

  22. Wow the low clouds cleared quickly. Got into the shower and it was mostly cloudy. Now the sun shining and it’s beautiful!

    • Punxsutawney (aka HIOPHIL) at work by Sunset High elev ~280' says:

      I actually got “misted” on while riding to work this morning; felt a bit like fall. I was worried that it was going to be cooler today than forecast, but mostly sunny on the westside of town now.

  23. bgb41 says:

    Brookings had an overnight LOW of 77 this morning. The overnight humidity never got any higher than 24%

  24. pappoose in scappoose says:

    Latest off the 7-day posts. Tell the truth Mark, you guys and gals (TV mets) get together and throw numbers into a hat (within a predetermined range), then take turns pulling em out for the days temps to forecast. Hahaah! KPTV wins the bravery award again!


    KPTV 88 90 87 88 92 95
    KGW 90 91 88 87 92 92
    KOIN 91 90 86 88 90 87
    KATU 90 93 88 89 91 93

  25. pappoose in scappoose says:

    Certainly will need to be relentlessly on watch for Stray Albino Donkeys meandering around:

    National Weather Service Portland or
    207 am PDT Friday Sep 2 2011

    One other issue late Sunday or Sunday night is a weak upper low off California begins to drift northeast toward southwest Oregon. Will need to watch whether that can spread any instability our way early next week…and it may take a bit to moisten up our dry air mass after the weekend offshore wind event. Tolleson/Wolfe
    Long term… Will need to watch whether a weak
    upper low off California that drifts into southern Oregon can create
    some instability near our forecast area…especially since this upper
    circulation gets lost under the Pacific northwest upper ridge and
    begins to meander around with little or no steering currents.

  26. Timmy_Supercell (Klamath Falls @ 4200') says:

    Indian Summer, here we come!

    • Karl Bonner says:

      I’m not sure if “Indian Summer” is the best phrase to describe mid to upper 90s in the first 10 days of September. (Come to think of it, what DO you call a period of very hot weather during “the season between summer and fall”; i.e. September?)

    • Margaret in Fairview says:

      I am so not looking forward to this.

    • Jbpdx says:

      It’s still summer!!

    • Ryan (Walnut Grove) says:

      Indian Summer doesn’t come into play until October. 🙂

  27. IF this comes to fruition and I have to say it’s looking a bit more likely, this will go down as one of the greatest heatwaves of September. I’m out…. be back for 12z(MAYBE 6z) …

    • Karl Bonner says:

      I hope Mark digs up some info on previous September heat waves to put this one into perspective.

  28. bgb41 says:

    9/1/2011 Oregon (All) Temperature Summary

    High:92 at BROOKINGS( 79 ft)
    Low: 61 at BROOKINGS(79 ft) & Brookings Airpor(459 ft)

    High:49 at HOWARD Mt Howard(8150 ft)
    Low: 15 at DESCHUTES PORTAB (5100 ft )

    Largest Diurnal Change: 59 degrees
    CABIN LAKE (79/20 ) (4560 ft )

  29. 00z Euro guidance

    850 mb temps for 5 pm PDT/highs at PDX

    Today: 13c, highs near 80.
    Sat: 19c, highs 89-93.
    Sun: 20c, highs 90-95.
    Mon: 20c, highs 90-95.
    Tue: 21c, highs 92-96. 590 dm heights by Tue night.
    Wed 23c, highs 95-100. 592 dm heights.
    Thu: 24c, highs 97-102. 592 dm heights.

    Depends on surface flow, I know….

    00z EURO 500mb/850mb
    HOT until Monday the 12th!


  30. With all due respect, and I do mean, with all due respect, Mark, I think you might, could be, possibly are still a tad bit on the conservative side, in my opinion.

  31. 00z GFS is not backing off, instead prolonging the heat wave until possibly the 12th…. 850mb peak +25c to +26c Depending on surface flow there’s a reasonable chance of 8-9 90+ days on the way…. I’d still be cautious with that though.

  32. Karl Bonner says:

    DLS stats for August: Hottest 98, coolest 52. Warmest low 73, coolest high 72. Widest diurnal swing 43, narrowest swing 14. Averaged high 87.6 (pretty much normal), averaged low 61.6 (about 3 degrees above normal), averaged mean 74.3 (about 1 degree above normal). Measured precipitation: zero.

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