An Early & Wet Fall Continues; Even Cooler Temps On The Way

7pm Thursday…

It was dry today!  No rain in Portland today, what a nice break after so many downpours the past week.   Don’t get used to the dry weather, it’ll be wet again after midnight, plus Sunday should be a soaker too.  Maybe more important, all our models are showing even cooler conditions to wrap up the last 10 days of September.

Summer “ended” on September 6th this year in our area; that was the end of reliably  warm & dry weather.  There’s no sign of anything above 75 in the next week either and our very wet September will continue…

The updated September numbers so far for Portland.

Rain PDX Last 10 Days

A rain total above 3″ in September has only occurred a few times the past 30 years.  In 2013, 2010, & 1996.

Take a look at some other spots around the region, some hefty totals in the Coast and Cascade Ranges

Rain Totals Metro Area

The entire region has been wet too.  The precipitation anomaly for the past 10 days

cpc_gauge-oregon-10day_percent_anom-5200000

What’s ahead?

Real quiet tonight through Saturday, but a strong onshore flow and a dying weather system gives us light showers tonight through the morning commute Friday.  Saturday still looks great, at least compared to what we’ve seen lately.  Partly cloudy with temps making it into the lower 70s; at least a little more reasonable for late September.

Sunday = a soaker as an upper-level trough moves overhead accompanied by a cold front.  The entire first part of the day should be wet, then it’s on to showers the 2nd half.   Monday should be reasonable as showers end, but cool with 850mb temps only around +5.  Even with some sunshine the best we’ll do is mid-upper 60s.

Weather geeks will recognize the weather pattern the rest of next week; a classic arctic blast setup for wintertime Wednesday through Saturday.   Look at the ECMWF ensemble 500 millibar height chart for next Tuesday.  A strong ridge attempting to build over and just west of the West Coast.  Heights go up to around 580 or so which is typically warm fall weather.  Yet there is plenty of fast westerly flow overhead which keeps us from getting very warm with lots of cloud cover and maybe even showers making it as far south as northern Oregon.

euro_tues_24

But see what happens by Thursday a week from now?  The ridge is retrograding (moving farther to the west) and building over Alaska.  That forces a cold airmass to move south through Western Canada.  You can see a cold upper-level trough dropping south around Juneau.  At this point it’s showery over us (although not stormy) and snow levels are heading down toward the Cascade Passes for the first time this fall season.

euro_thurs_26

Then two days later…Saturday the 28th.  This is the pattern we had in February with cold (cool in September) Canadian air pouring south into the western USA.  A strong ridge is…wait for it…parked right over Alaska and the eastern Pacific.   Hmmm, just like February and parts of this past summer.  Interesting.  This pattern is not very wet and could give us partly cloudy skies with daytime highs in 60s and lows in the 40s.

euro_sat_28

I’ve only shown you the ECMWF ensemble maps, but the Canadian and GFS are very similar.  September will likely end cool.  The previous run of the ECMWF showed this similar “dipole” of a chilly western USA and warm east continuing into at least the first few days of October (through the next two weeks).  Surface temp anomaly from September 29th through October 6th…

sfcta_week2_bg_NA

The effect is clear; the 15 day ensemble low/high temps for Portland are almost all well below average for late September and early October

gfs-KPDX-gefs_downscaled-8916000

Summary

  • We are done with “summer weather” and even any significant warm & dry spells.  At least through the end of this month.  We can have spells of warm & dry weather in October, but that comes with nights in the 40s and highs in 70s; definitely not “summer-like”.
  • It won’t be quite as wet the next 7-10 days, but we could easily see another inch of rain or more in the next week
  • A first frost is likely many areas east of the Cascades within the next 10 days, and possibly a few of the coldest areas in Western Oregon and Southwest Washington.
  • Timberline Lodge at 6,000′ will likely see its first snow of the season about a week from now.  Snow may get down close to the Cascade Passes (briefly) too.

Chief Meteorologist Mark Nelsen

28 Responses to An Early & Wet Fall Continues; Even Cooler Temps On The Way

  1. Roland Derksen says:

    Classic early fall soaker here today; Rain began last night shortly after 9pm, was pretty light until after 7am, when it really started to pour. I estimate about 1.6 inches at this time since it began.

    • Roland Derksen says:

      a total of 1.82 inches for me yesterday. Doesn’t usually get much wetter than that on a September day, but the wettest was 33 years ago (sept.23, 1986) with 2.83 inches.

      • On the damp side here fifty miles to your south, but not drenchingly wet. It could be cooler in my book. Highs are still in the 60’s F. I’ve seen them in the 50’s in the lowlands by this time of year before. I hope to finally make some time for mushrooming this week. With all the moisture, I’m hoping it’s a good year.

  2. Larry says:

    Gosh, now looking back at early September, I recall seeing groups of geese flying southeast on three occasions. The groups were disorganized and looked like they were in a hurry. Sort of like rush-hour traffic in Portland. Maybe the geese were leaving before the cold blast hits Oregon??

  3. Andy says:

    Watched an interesting video from space weather people. They explained how low solar affects the jet stream strength. During times of low sun activity you have an erratic up and down jet stream. It is more prone to be stuck in certain patterns…Omega Blocks…droughts and flooding and arctic outbreaks in lower latitudes. When we have high Solar we have a strong jet stream…less up and down motion. This has a tendency to lock cold air up north…less warming in the poles. They showed strong evidence from historic weather data. They feel we are entering a interesting time in our weather patterns. They also mentioned with the melt up north…this will dramatically change are ocean temps down the road to colder. I guess time will tell.

    • MasterNate says:

      Link?

      • Andy says:

        Found it by accident on You tube. I guess they have frequent updates. I found it fascinating the info they showed…makes you question the factor the sun plays in our weather.They did explain how low Solar plays a role in our planets temps…but not the way a lot of people think.

  4. paulbeugene says:

    end of this week looks like it did at the end of September 1971.
    Time to dust off the F R O S T

  5. Joshua Lake Oswego says:

    High res models backing off on Sunday rain. Maybe .10 – .20” on average for the metro area.

  6. Roland Derksen says:

    It’ll be intresting for me to see when the first frost (and freezing minimum) will occurr.Last year it was on November 12th, but it can be a few weeks earlier if conditions are right.

  7. Andrew says:

    I too am curious if this pattern which really emerged in February and has resurfaced again will persist into winter. Is there any historical basis for that occurring? Does a general pattern in late September foretell anything for Dec-Jan typically? I’m trying to think back to fall of 2018 and whether general trends then aligned to our dreadfully boring weather in December and January.

  8. Jason Hougak says:

    Absolutely love it, keep it coming!

  9. Evan -- Cedar Mill says:

    Hopefully this is a good sign for this winter…

  10. Gene says:

    It would be nice if we could get this kind of arctic pattern in December or January instead of September (accompanied by a decent amount of moisture, of course)

  11. ocpaul says:

    It seems to be, that Nov-Dec are seldom like Sep-Oct. And, who knows about Jan-Feb. The ENSO is neutral for the next 6 months.
    But, so what? No body tells the weather what to do. Fingers crossed for cold/wet. (till April)

    • JohnD says:

      Aren’t “ENSO neutral” years statistically most favorable for low elevation winter weather? At least that is what I have always thought. Of course no two years ever the same–so who knows?!

  12. Hopefully the warm ocean doesn’t screw up our chilly nights next week!

  13. tim says:

    Why can’t we get this pattern in December or January anymore, it’s like there’s some force that won’t allow it to happen, figures.

  14. Shaun says:

    Thanks Mark, I live on the east side (Redmond). I really appreciate your blog!

    • High Desert Mat says:

      You have a neighbor Shaun. I’m in Redmond as well. Hopefully we can score something half of what we saw in February. That’s all I’m asking for this winter. We’ve had some doozys the past 6-7 years or so. So I’m being greedy. Lol

  15. Ken in Wood Village says:

    Thank you Mark for the update. I believe this pattern will persist and I believe it will go all the way into winter. I think fall/winter of 2019-20 is going to be something to remember. 🙂

  16. Mike says:

    Thank you Mark. So cool to get a good perspective about recent weather. Best reports are here, that’s for sure.

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