Weekend Rain Slow To Arrive = Drier & Warm Friday

8pm Wednesday…

I’ll be on vacation and out of town Thursday through most of next week, so here’s a quick update. It’s too bad I’ll miss the first soaking of fall this weekend!

Here’s the plan:

  • The next two days (Thursday/Friday) will be all or mainly dry from Portland south and east. Temperatures warm into the upper 70s the next two days too. There COULD be a sprinkles or a light shower during the daytime Friday, but that’s it.
  • Real rain, “the soaking”, doesn’t begin until sometime after sunset Friday evening. At this point it appears high school football games could be dry; or at least you shouldn’t see any downpours
  • The bulk of heavy rain (about 1/2″ in western valleys), falls Friday night through early Saturday morning.
  • Showers continue off and on Saturday, although they may not be very intense. Expect the usual downpours, then sunbreaks, then a rumble of thunder etc…
  • Sunday appears to be the wetter of the two days this weekend. More frequent and intense showers are likely. This can be the setup where we get funnel clouds too.
  • It’s back to warm and dry weather most or all of next work week. This is a “one-shot” deal, not the beginning of a cool and wet period.

In general, weather forecast models have been in good agreement on the wet pattern this weekend. A cool and broad upper-level trough settles over the Pacific Northwest late Friday through Monday. You see the much lower than normal heights (around 18,000′ up in atmosphere) midday Sunday.

Ahead of that cool trough, a wet Pacific frontal system first aims at Washington state on Friday. This is the change the past 24 hours. Originally models were thinking the system would be farther south to start. But now it’s obvious just about all rain remains in Washington on Friday. THEN, Friday night and Saturday it slides south through Oregon. In the end our total rainfall is still the same mentioned (previous blog post) a few days ago; about 1″ or so in the western valleys by the time we dry out Monday. This is the morning ECMWF model. It’s interesting that both GFS and ECMWF ensembles show about 1.5″…good agreement.

And you see the widespread 2-3″ in the Coast and Cascade ranges. This will put Fire Season 2021 partially into the grave. There won’t be much left of those fire complexes burning on the west slope of the Cascades.

Sunday’s snow level (the lowest elevation we’ll see sticking snow) in the Cascades is close to Timberline Lodge…could be a mix there, or even a dusting by Monday morning. But of course it’s too early and too warm for pass elevation snow.

After a few leftover (light) showers Monday, it’s back to mainly or all dry weather next week.

I see about 1/2 of the European’s model ensembles generate measurable rain again AFTER this weekend in the last week of the month. But 1/2 do not. It would be perfectly normal to see a round of showers again in the last week of the month. That said, my gut feeling is that the last week of September will be much improved from this coming weekend!

Enjoy the rain this weekend! After 3 months of dry weather, FOLLOWING the driest spring on record, we desperately need it. I will be back at work that last weekend of the month.

Chief Meteorologist Mark Nelsen

110 Responses to Weekend Rain Slow To Arrive = Drier & Warm Friday

  1. Anonymous says:

    Rain started here in LO a couple of minutes ago.

  2. Anonymous says:

    Sunny and 74 so far today. For the season so far we have had 42 days of at least 90, 103 days of at least 80, and 142 days of at least 70. Most assuredly our hottest Summer since the start of records in 1892. After a couple of wet days to start the week next weekend looks to be warm and dry. Mid to high 70,s. Summer like weather rolls on. Peace.

  3. tim says:

    Lots of upwelling along the coast does anybody know the reason?.

  4. tim says:

    I don’t think that will be the last of it for pdx, another warm up next weekend upper 70s at lest.

    • Anonymous says:

      We have plenty of days in the 70s, even a random day or two in the 80s, in October in Portland. It’s not unusual.

      • Zach says:

        Yes, specifically the 1st & maybe 2nd week. End of October is completely different will the average high down to like 58F I believe. Oct is the most dynamic month of the season in our climate.

  5. Paul D says:

    Yesterday made the 90th 80+ day this year. Another heat related record broken….

  6. Roland Derksen says:

    I think we have here a good shot at getting a new record for the wettest September on record, if the next 5 days go as forecasted. If not, it’ll definetly at no.2.

  7. tim says:

    What a contrast 76 in seattle and 89 in pdx today what difference a few miles make.

  8. Anonymous says:

    Rain totals falling apart some. We’ve seen this before…

  9. Anonymous says:

    Mark’s newest rainfall map shows the Portland metro area getting anywhere from 1.5 to 2+ inches late Sunday night through early Friday morning. Eugene scores big with 3 inches.

    • tim says:

      A wetter then normal September could lead to a dryer then normal October this reminds me of 2013 very wet sept followed by a dry fall.

      • Anonymous says:

        Looks like as of today, October will start out cooler and by the end of the month be average/slightly warmer. Above average precip all month long though! That could easily change between now and then, especially with how things seem to be going now.

  10. Oliver Watson says:

    Euro is backing off some on rainfall totals. It’s going more the way the gfs was a day or so ago. I don’t think euro is King anymore. From what I’ve seen over the last few years is the two models play games where one will show something when the other won’t and then when the other starts to show the same thing then the other changes its tune and goes in the opposite direction. I really don’t think either is consistent in showing the truth 5-7 days out or even 3-5 sometimes for that matter.

    • Anonymous says:

      That’s because they’re using very little – if any – real machine learning or deep learning algorithms. Which means the models can’t learn from previous mistakes and learn new patterns. As climate change accelerates and causes permanent modifications to our weather systems, the models will lose even more accuracy. The good news is the Euro has outlined machine learning as a goal for their 2021-2030 roadmap. Still I doubt it’ll be as robust as it needs to be. They’ll need silicon valley for that.

  11. Anonymous says:

    The summer weather is finally dead after Saturday unless that SoCal heat works its way up here that first week of October, but it’s looking unlikely. 00Z Euro is holding steady with >2in of rain Sunday-Thursday.

    I’m interested to see if this intense level of back-to-back storms that are breaking their way through will last into winter. Would be nice to get some moisture packed cold fronts slam us in December for once.

  12. Anonymous says:

    00z GFS has the area getting about 1.25-1.5 inches Monday through Wednesday

  13. Roland Derksen says:

    I’m seeing rain symbols for Sunday through Tuesday here for the next week. This September already has about twice the normal amount of rain for us. It doesn’t look like we’re going back to dry and warm.

  14. Anonymous says:

    “It’s back to warm and dry weather most or all of next work week. This is a “one-shot” deal, not the beginning of a cool and wet period.”


  15. Anonymous says:

    12Z Euro is looking very nice with precipitation values. Too good to be true perhaps

  16. Andy says:

    Forecast bust here in Albany…Thunder and down pours. Much stronger system than models were showing.

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