Cooler (And Normal) December Weather Is Here To Stay

9pm Friday…

December arrived with record warm temperatures across the region. Wednesday (the 1st) was the warmest December day we’ve seen in Portland since 2015! These are just a few of the records set that day. Notice several spots in eastern OR/WA set all-time December high temperature records.

Cliff Mass (UW) in his blog called this the 2nd great Northwest heatwave of 2021. By that he means that many areas east of the Cascades observed “heat” just as anomalous as the June event; 25 degrees or more above average in spots.

We cooled off nicely today after a cold front passed through yesterday morning. Highs today were back in the 40s along the I-5 corridor…much more seasonal.

What’s ahead?

The mild/warm westerly flow in the upper atmosphere is changing to a setup where cool troughs dig down from the northwest, passing through our region. Each one should spin up some sort of wet system. So we can expect precipitation regularly over the next 7-10 days. Here’s the view Saturday

Then Monday; another trough passing by

Then a third next Wednesday

Looking farther ahead, to Monday the 13th, models GENERALLY have more troughing digging into the eastern Pacific.

In general this whole setup the next 7-10 days is cooler than normal. At this point I don’t see any surge of cold arctic air moving south, but it may be close at times. This chart shows things well. It’s the ECMWF 850mb temperature ensemble chart. It shows temperature (C) around the 4,000′ elevation for the next two weeks. Green line is the average of all 51 ensemble members. I’ve drawn the yellow highlight at 0 degrees.

Basically for pass elevation snow in the Cascades it needs to be at/below that yellow line. That’s the case most of the next two weeks…very good. Finally, we’re going to see a snow base develop in the mountains, and it’s not going anywhere this time.

Lowland Snow?

It’s that time of year! The next 2.5 months are primetime for snowfall in the lower elevations of NW Oregon and SW Washington. I’ve got a few thoughts on that. The pattern I’ve shown above CAN bring snow to the lowest elevations of the region, but right now it doesn’t appear to be quite cold enough to do that. Sure, late next week 850mb temps dip to around -6 or even -7 at 850mb. That means foothill snowfall for sure (1,500′ or higher). But it takes more than that to get any sort of widespread snow event to the valley floors. I’m not saying we won’t see snowflakes at some point in the next 10 days, but nothing really sticks out on the maps right now. Note there is almost no support for significant snowfall from ECMWF ensemble members in the next 10 days. This is for Aurora/Canby; I chose a spot in the middle of the valley to avoid low resolution modeling issues. Ignore anything beyond 10 days…it’s a crapshoot after that.


  1. There’s no sign of a cold “arctic blast” the next 7-10 days. My exposed chicken coop waterline will remain on for now. Beyond that, the 15th and after? Who knows!
  2. I don’t see any sort of widespread snow/ice in the lowlands in the next 7-10 days. I haven’t put my snow tires on yet and don’t plan to for now. However, I would not be surprised to see flakes mixed in with rain at some point during that period. Or even a brief snow on the hilltops…maybe.
  3. It’s quite possible we see at least some partial ski area openings NEXT weekend, the 11th/12th

That’s it for now. Have a great weekend!

79 Responses to Cooler (And Normal) December Weather Is Here To Stay

  1. runrain says:

    NWS Sacramento calling for “a few to several yards of snow” with the upcoming storm in the Sierra.

  2. Jake says:

    Seeing a lot of potential ahead for snow. The end of December to mid January is peak season for PDX. With the overall window being into mid February as many know.

    With that said long range models have hinted at something at the end of their runs for along time now. Which means nothing until the 5 day window but it is indicative of the kind of Winter we’re experiencing (more extreme on a lot of fronts).

    I think with that said I’ve noted an active Winter over much of the Northern Hemisphere. French Alps were hammered well early November, Siberia has seen arctic blasts and Alaska as well with some Nor’easters for the East coast. We’ve largely been left out except for the slightly above average rainfall for a few months that didn’t want to stop for a moment there (weather I love!).

    The next few weeks will show if we classically just see NW flow for above average snowfall in the Cascades typical of most mod/strong La Niñas or more down in the valley. I’m going to keep a close eye on the next few weeks as it involves a lot of my family members with work outdoors unlike myself.

    I think we see snow in the next 3 / 4 weeks if we do see it, raining right now in L.A. Cali., Winter is upon us! My 2 cents.

  3. Mountain Man says:

    1 1/2 here now. Nice winter wonderland up here in the Foothills and still snowing heavy off and on. It’s down to 31.5 degrees so I’d guess some flakes are making it down to perhaps 500 ft considering I’m at 1400 ft.

  4. tim says:

    8 to 14 hazards outlook has the west slight chance of much below temps, not sure if that’s artic cold or just a cool pacific trough along the west coast, anyone know?.

    • Anonymous says:

      That’s a strange way to say the CPC is just throwing darts.

      The CPC’s “slight” chance = 20% for those that don’t know. Considering how often they’re wrong, 20% is generous

    • Andy says:

      I think were in the 70% percentile for colder weather according to the CPC…were trending colder…some climate models show the NW in a Northerly flow out of Canada due to high pressure over Alaska later this month…though it could change with how they have been performing lately.

  5. Rick says:

    1/2 inch of snow @ 1000 Ft – North coast range

  6. Mountain Man says:

    Nice half inch of snow up here and coming down pretty hard at the moment. I’d comment a picture if I knew how.

  7. Snow-Zone Dallas/400ft Roman says:

    Amazing we had a little snow shower over night. A little snow slop still on the roofs. Barely but it happened. First official snow this season. Let’s go for a big Arctic blast next few weeks!

  8. Ken in Wood Village says:

    Well, the National Weather Service has started mentioning rain and snow in the forecast starting Monday night 🤔🤗❄ snow level isn’t at sea level but it’s low enough to start seeing it fly in the air 🤗❤ We’ll see if those levels get any lower 😉🌬❄☃️⛄

  9. Already down to 36.3 at my place, 850 temps -5, if we get a cell to come through, we would have a bit of cooling, and then if another cell came through,we could MAYBE see some flakes, but thats a VERY big maybe, the setup will have to be perfect with great timing for it to happen. I would also be asleep if it happened.

    • Mountain Man says:

      Not going to happen Hank, temp up here at 1400 ft hasn’t moved more than a half degree in 4 hours though we continue to get very light ice pellets hovering around 34-34.5 degrees. Showers are too light to bring any cold air down and clearing to minimal between them.
      I’d love your, or anyone’s thoughts though however on one heck of a sharp cold front on Saturday. I’m starting to think that will be an interesting 6 hours of weather. Could even bring snow briefly to sea level somewhere west of the Cascades if it moves slowly enough! Haven’t seen one looking quite like that in a few years!!!

  10. Mountain Man says:

    Okay just chiming in, got my first real snowfall mid afternoon today, just flocked the branches and grass a little, maybe a shy 1/4″ and melted back up the mountainside a few hundred feet within an hour after the shower. Still, was nice to see, analyze the current atmosphere and remind me what it takes to get snow to my elevation. Snow stuck on some objects down to 1300 feet briefly a bit below my house. Location, foothills of Mt Rainier.

    • Mountain Man says:

      By the way, I’m probably about equal distance north and east of Portland as it seems like say someplace like, Detroit lake is south and east of Portland. It seems like so many of you are scattered down the valley. If anyone ever wants to ask me, point blank ask me as long as you are kind. I have the same atmospheric degree as mark from the same school. I look at all the ensembles form every model everyday from Eugene to Bellingham. The only reason I don’t bother commenting, there’s a few of you who are jerks, not most of you, and makes me feel like my voice is pointless. I usually will answer though if asked. Happy winter guys!

      • Ken in Wood Village says:

        Hi Mountain Man 🤗 I’m happy to hear from you again 😊 You probably will see more snow because the snow level is going to stay low for awhile. Mark said people in the Westhills could see snow flying in the morning.

        Just looking at the models, snow levels look to stay low for a long time. The GFS model was showing the really cold 850 temperatures going back up into Alaska for the past couple of days (I didn’t understand why it would just hundreds of miles in a day) and so I wasn’t believing what the GFS was showing until last night (I think it was last night). Now it’s more a lined with the Euro model.

        Today was probably the last 50+ degree temperatures we could see for probably a week or more. There are some borderline snow events coming up in the next week so I think we need to keep an eye on the models on were the track of those lows go. Saturday looks to be a very active day. A lot of rain with gusty winds and when the cold front moves through, that snow level looks to fall a lot again.

        We’ll have to keep an eye on how this all plays out. Again, good to hear from you again 😉🤗❄

        • Mountain Man says:

          Aww, thanks Ken. I could comment on the 5 ways snow can make it to the valley floors, sometimes simplified to three for the public which is inaccurate… because one of the 5 is looking likely next week though borderline… But simply the one you know too well, you know whenever it’s cold enough, the coastal mountains eat the precipitation or the offshore low-level flow does. Take your pick. Both are showing up as most likely in the 5-8 day area. The only obvious take is, not warm and/or wet.
          That little tease today sure made me want more. I think I’ll get pretty white up here at times this next week, but no snowstorm even for me…

  11. Zach says:

    Ski season begins this Monday.

  12. Weatherdan says:

    50 and mostly sunny at 2:00PM. What happened to the falling temps and heavy showers that were forecasted? Lately the TV mets seem to get it wrong a disturbing amount of the time. Peace.

    • Jim says:

      And you complain a disturbing amount of time

    • Ken in Wood Village says:

      It may take awhile to get to you. Temperatures have been falling in the Portland area. It was 52 this morning and it’s 45 now. I think we’ll be in the upper 30’s by midnight or so 😉

  13. Anonymous says:

    Thanks guys, you’ve got me all anxious over that earthquake swarm on the Juan De Fuca ridge now

  14. tim says:

    12z gfs artic outbreak on the 24th this time it’s a lock because it’s hour 384.

    • Zach says:

      lol. Yup it appears the hammer is about to drop at the end of that run. Too bad its entirely fictional at the moment.

    • No doubt, it will happen.

    • Andrew says:

      What’s the deal with GFS constantly showing cold/snow at very end of runs. I understand models are basically worthless this far out but weird it always defaults to cold/snow versus a more typical conditions. Worth noting, ensembles don’t support.

      As of now and taking models for next week at fave value, I suspect we may see flakes in air mon-tues. It’s not our true snow pattern but 850mb temps appear to hover in the -5 to -7 range, enough to at least give us some mixed precip down to sea level. At least that’s my read. Of course by weekend, even the slightest moderation of those temps and that chance is gone for anyone below 1000-2000 feet.

  15. Roland Derksen says:

    Clearing skies and windy conditions here this morning. Looks like a sunny day is in order. It’s still early in the month, but so far I like this December. It’s normal!

    • W7ENK says:

      Oh, and the person who keeps trying to hack my WordPress/Gravatar login can stop triggering my net security tools now. I have your IP, and I’ve “Neotrace”-ed it right back to the basement PC you think you’re hiding behind. You’ve been reported, and if it keeps up, expect a knock on your door in the middle of the night. Your dad and stepmom probably won’t appreciate the racket. 😉

    • Oliver Watson says:

      I learned my lesson about 10 years ago

  16. Andy says:

    The 11th quake just hit…5.5 off the coast

  17. Andy says:

    10 earthquakes off the Oregon coast today… the largest was a 5.8.

  18. Weatherdan says:

    Let’s face it, we have entered a new era. Mild Winters and blazing hot Summers. California has arrived in Oregon. Will we see valley snow this Winter? Maybe but each mild day that passes makes that less likely. I am hoping for snow but feel I will be disappointed. Merry Christmas one and all. Peace.

  19. Andrew says:

    Lots of snow signals again in ensembles for early next week. heavy majority of members. I learned my lesson and used Aurora Airport this time (thanks Mark). Totals aren’t significant and clearly inflated nonetheless, but makes me think there is at least an outside chance we see snow in the air at some point, late night or early morning. Temps will be generally well above freezing at surface. Alas, no sign of an actual cold/snow pattern in models.

    • Roland Derksen says:

      I measured 2 inches up here in Vancouver (BC) yesterday, but most of it is gone now. Nevertheless, it’s my earliest snowfall since December 5, 2016, so that’s worth mentioning.

    • Andrew says:

      GFS 12Z does hint at the dreaded December inversion pattern about 10 days out. Models shouldn’t be trusted that far out but this pattern has become such a December staple for several years running I’m inclined to plan for it. Just hope it doesn’t last long.

      • Zach says:

        Yeah, but there is currently no ensemble support for an inversion so am doubtful.

      • Andy says:

        Noticed the same High pressure over the NW in the long range in several models…the only problem is you cannot trust anything currently.
        I think Mark probably won’t post anything interesting until things shift toward northerly pattern…Pacific flow is keeping things mild here in the valley…

  20. Christian says:

    Will it snow up at Bald Peak Thursday or Friday?

  21. Andy says:

    NWS info from this evening… northwest Oregon with snow levels
    likely to hover between 1500-2500 feet for much of the Wednesday
    night and Thursday time period. There remain a few colder ensemble
    members that bring 850mb temperatures down to ~-7C across the area so cannot rule out snow levels dropping into the 500-1000 ft range yet. Maybe some hilltop snow…

  22. tim says:

    18z gfs looks cold and snow at end of the run always at the end and also it’s the drunk 18z

    • Joshua Lake Oswego says:

      This weekend is looking pretty interesting too on the 18z GFS. Plenty of QPF to work with. Looks quite a bit too warm throughout the atmosphere though for a snow profile.

      • Ken in Wood Village says:

        I was looking at Saturday. It looks like it could be a very windy day. It would be a South wind so it wouldn’t support snow but cold air does filter in after the front moves through. That’s if it verifies 🤔

  23. Oliver Watson says:

    It’s crickets on this blog. Looking at the models makes you understand why. I actually stopped looking at them past 7 days. I notice even at 7 days out you have to take it with a grain of salt. Each day it gets closer to the event it warms up and drys out. It’s a sad state of the inability of these models to do their job

    • Anonymous says:

      It’s the same thing every year. Something juicy comes up on the models 10+ days out. People get prematurely excited and some are accused of wish-casting. The day finally arrives and it’s the same ‘ol cold and rainy, business as usual stuff. Then the place gets quiet for a little bit as reality and disappointment sets in.

      No worries though, it’ll come back to life soon.

      • Andrew says:

        Very true. I think the key is to ignore anything slightly better than a “marginal” cold/snow pattern beyond 5-7 days out. Those almost always regress back to typical conditions. But more extreme events often do start showing up in advance. They often start so extreme that even with the standard regression, we’re still in the zone of action. This came to fruition last February. Models started hinting at the cold stretch many days in advance. The early trends were ridiculously extreme. feet of snow, negative temps at sea level. By the time we got to the main event it was clear all that wasn’t going to happen but we were still going to get hit. Therefore, i really only pay attention to the real obvious signals and assume everything else is just the standard model bias in our region told colder and wetter. It’s still fun to follow the marginal events from an anticipation standpoint, but i’m usually looking for them to evolve into the extremes versus banking on them to deliver anything on their own.

        • Oliver Watson says:

          It seems like that logic also applies to just a typical rainstorm anymore. If it shows an inch 7 days out be ready to only get a quarter of that. It’s rediculous! I’m a window cleaner if my expensive tools I use only get the window 25 percent clean and I have to use Paper towels and Windex to clean the rest what good are my blasted tools. We have to extrapolate so much on these models 5-7 days out that it makes the models worthless in my opinion. I say they scrap long range weather forecasting and focus on getting it right at a 3 day window. Their money would be better put to use that way

        • Joshua Lake Oswego says:

          Well said, Andrew. The crazy thing is that the June heatwave verified almost to the extremity that it was forecasted to. It seemed impossible seeing temps of 120-122 being thrown around by the GFS. If we could get the cold or snow version of that, it would sure be something.

        • Joshua Lake Oswego says:

          I feel you pain, Oliver. I half-jokingly like to say that you should use the 10th percentile for QPF on the GFS or Euro ensembles when more than a few days out. It actually seems to be somewhat accurate.

        • Evan -- Cedar Mill says:

          Exactly, unless the models are showing below zero temps and feet of snow, nothing is happening. And even then, cold/snow is far from a guarantee.

  24. Ken in Wood Village says:

    Interesting, some people are close to freezing right now 🤔 I also see from observations, they have a Northerly to Northwest flow. I think we could see either snow or rain and snow mix or chunky rain 🤗❄

  25. tim says:

    I see the cfs has gone quit cold for us here mid december unless im reading it wrong.

  26. Ken in Wood Village says:

    I was looking at the radar and I think the weak cold front come through a while ago. Temps should be falling through the night. I was just outside, and it feels cooler now.

  27. Cookie M says:

    Thanks everyone

  28. tim says:

    Hate seeing the cold pdo getting gobbled up by the warm blob but maybe the cold blob will fight back soon.

  29. OC550 says:

    Thanks for the blog post Mark. Glad we have some interesting weather ahead and snow at least for the mountain.

  30. W7ENK says:


    Anyone care to venture a guess as to where this weekend forecast is for?

  31. Randy says:

    I love the “who knows” comment. That my friends is a true statement.

  32. PDO Finally released, its still -2.71, which would make it the 3rd coolest November PDO ever. And for the October 1955 EXTREMELY cool PDO we talked about, the next month actually had a warmer PDO than us.

    No surprise, Tim overexaggeted the warm, it was actually much less warming than normal.

  33. Diana F. says:

    Yes! It is finally here! So you’re telling me there’s a chance? ❄️🏃🏽‍♀️🚘🥬🧻🍞

  34. Roland Derksen says:

    Some snowflakes seen here this morning, but the air is still just a bit too warm; 34.5F for a low. There are more chances for seeing snow in my location coming up, but we’re not yet into real arctic air.

  35. ellen sanders says:

    How about further up north? Canby is quite a ways from Kelso. Looks like WA is much more blue…Any  thought? Thanks for updates, I do appreciate them. Ellen

  36. JERAT416 says:

    Thanks for the update Mark !

  37. MasterNate says:

    White Christmas this year. Fork it.

  38. Rick says:

    First- Thanks for the update Mark

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