One Last Christmas Break Snow Chance Early Thursday

1pm Wednesday…

It’s been a fun ride, if you don’t mind driving in a little snow and/or didn’t need to go anywhere the past week. We’ve seen several little (or big depending on location) snow events. Of course the largest and most widespread was Monday night through Tuesday morning. Officially PDX picked up 2.5″, which now means it’s the snowiest December since 2008 in the metro area. We were overdue for a cold & snowy spell in December, they’ve been very mild lately. Although we still haven’t seen a regionwide outbreak of cold arctic air.

That cold modified arctic airmass has once again surged south and through the Gorge, into northern Oregon. At noon we’re barely above freezing in Portland with a chilly east wind blowing on the east side of town.

That cold east wind isn’t too strong, just about 5 millibars from The Dalles to Portland pressure differential. Weak sauce… right now things look like this as sea level (black lines, not the colors). Cold high pressure sending easterly wind into NW Oregon/SW Washington and a weak area of low pressure forming near Haida Gwaii

That low slides down the coastline, like previous ones have, but this time it goes inland NORTH of us. Looks like this around 10am Thursday. You like my 3rd grade drawing skills?

We get a relatively strong southerly wind later tonight through the first half of Thursday. That means the cold arctic air is replaced by a much milder airmass (temporarily). Snow levels lift up to around 2,000′ or so by midday. All models support the idea of a quick late night warmup from Portland south and all along the coastline. We’re going for a low of 23 in Portland tonight, but that’s before midnight. I expect temperatures to be around 33-34 by 7am across most of the metro area. Precipitation from this system starts as snow which will stick in some spots from the Portland metro area north. South of Portland I think sticking snow is unlikely (including Salem). The cold air sometimes lingers longer than expected in the Longview/Kalama/Woodland/St. Helens areas in this setup. I’ve seen it before. I think that’s where a quick 1-2″ is more likely.

After 10am or so precipitation turns to light showers, mainly rain in the lowest elevations. Most models look something like this

SUMMARY

  • It’s unlikely this will be a significant snow event in the lowest elevations from Portland/Vancouver southward, especially after what we’ve seen the past few days.
  • Sticking snow begins between 5-8am from Portland/Vancouver area north, but for most of us I don’t expect much road accumulation due to rising temps. Snow will still be in the air for a few hours though; it may look quite snowy. I am forecasting NOTHING TO 1″ ACCUMULATION, BEST CHANCE FOR STICKING NORTH OF PORTLAND

METRO AM COMMUTE: Spots of leftover snow/ice on roads from overnight freezing, possibly a few spots of new snow, but not much. Temps rising from 32 around 6am.

METRO PM COMMUTE: Totally clear roads, except leftover snow/ice way up in hills, and possibly northern Clark/Cowlitz counties. Temps in the upper 30s.

COAST/SALEM/ALBANY: Likely clear roads & no snow tomorrow

GORGE: Snowy morning, 1-4″ new snow by midday. I-84 may be icy/snow first half of day

The low pressure system and upper level flow is perfect for heavy snow in Cascades and the Blue Mountains. Tomorrow is not a good day for travelling I-84 east of La Grande or through Cascades passes as you can see in the accumulation graphic above.

Just like Tuesday night and this morning, that chilly arctic air will attempt to surge south by Friday morning. But it won’t be quite as cold. Expect lots of clouds and temperatures only in the mid 30s Friday. New Year’s Eve should be just fine weatherwise, unless we get scattered icy spots on the roads. You can see that chilly high pressure back in control at 10am Friday with more of those nice hand-drawn features. BTW, I think in high school art class I got a C at best…really! Hmmm…

Friday/Saturday will mark the end of the cold northwesterly flow we’ve been in for about two weeks. Here’s the view overhead tomorrow

By Monday, we’ve transitioned back into an active westerly jet stream again with various model solutions for next week. All of them are wet.

Sometimes we get a big snow/ice event at the end of a cold spell. That’s when we get a deep upper-level trough offshore and low level offshore (easterly flow). That’s not happening this time. It’s a relatively quick change to southerly wind Saturday through Monday. When solid precipitation arrives later Sunday and Monday, most likely it’ll be rain. But this means even MORE snow in the Cascades. Snowpack is now well above average in many parts of Oregon. Very good news!

That’s a wrap for 2021. I’ll be off Thursday-Sunday so no blog posts until early next week. Stay safe in your travels.

Chief Meteorologist Mark Nelsen

291 Responses to One Last Christmas Break Snow Chance Early Thursday

  1. Andrew says:

    Should be a fair amount of snow cover to our north and east should we get a more favorable cold pattern by end of month. That’s one advantage of the later season offshore events – can be lots of snow covered land for air to traverse

    • JohnD says:

      Right on with your obs Andrew—we all enjoy them. Woulda-coulda-shoulda syndrome in life, sports, weather—Portland did miss out on the heavy hitting action this time. But we all know that many in the near by surround scored majorly just fine. I honestly think we’ll get some more low elevation action this season. So much volatility this year.
      As you allude, here’s pulling for a major retrograde of the imminently ensuing pattern—within a couple of weeks.
      And I can say one thing for sure: Today was an absolutely classic Portland, Oregon winter day: Dark overcast, low 40’s temps and drizzly rain all day (with maybe a wet snow plop making it through to the windshield now and then for good measure—and with a little imagination!)

  2. MasterNate says:

    Strong negative PDO hanging around awhile. -2.73 for December.

    https://www.ncdc.noaa.gov/teleconnections/pdo/

    I think our chances for more action are better than not.

    • Zach says:

      Yeah, at the very least it promotes cooler nights and I think lesser chance of big heatwaves.

      • MasterNate says:

        Yes, it would be nice if it stayed negative through the upcoming summer. Those muggy nights are the worst.

  3. tim says:

    The cansips has el nino developing next fall with a negative pdo but that’s not possible with el nino’s i expect that to change to a positive pdo as we get closer.

  4. Andrew says:

    Interesting to see the approaching low make one more feeble effort to pull in that cold air. This powerful warm front should officially close the door on what ended up being a more than two week run with arctic(ish) air hovering over our region. Disappointing that Portland area didn’t see more action but just way it goes. I am still hopeful that the imminent ridging episode transitions into a cold pattern as we transition from Jan to Feb. Until then and after a very wet next 24 hours, enjoy the bore.

  5. lurkingsince’14 says:

    Ugh inversion? So is our AQI is gonna skyrocket next week? 😞

  6. Andrew says:

    The death ridge is holding on strong in models but one minor consolation is there are some early signs in ensembles of high moving west around the 20th exposing us to the “real” cold. Will change a ton between now and then but at least some light at end of tunnel.

    • West Linn 200 says:

      Which ensembles? The extended euro models keep us average or slightly above into February. 850mb never gets below -4 over the next 10-14 days from what I saw earlier. I haven’t checked the latest euro ensembles yet though

      • West Linn 200 says:

        With the exception of Saturday – which does hit below -6 (although it’s dry) – I didn’t see the euro ensembles go below 36 degrees through the 18th at least. Most days are at or below average surface temps with warm air. Any kind of winter “event” in January seems unrealistically optimistic at this point. We tend to get lucky in Feb though as others have been pointing out 🤷‍♂️

        • Jim says:

          Guys I just checked the calendar. It’s Jan 4th! Yes all signs point to ridge over us starting this weekend but going out past 10 days is a crapshoot. This barely takes us to the middle of the month. Beyond that is anyone’s guess

      • Andrew says:

        The pattern change appears to start around that 14 day mark. i’m not really even looking at 850mb temps that far out. just focusing on the ridge sliding off to our west which is closer to our ideal cold setup. need the cold to load up north before then. I’m reaching here man haha. But when the ridge/inversion sets up, you got to go deep.

        • West Linn 200 says:

          lol fair enough. FWIW I hope you’re right. I wouldn’t mind another shot at sleddable snow sometime this month (and Feb)! One good burst of 4″+ quality snow would be ideal

  7. Roland Derksen says:

    A few snowshowers here this morning, but nothing that is sticking for long- it’s all slush now. Tomorrow night/thursday morning could be quite a different story. We could see at least 6 inches here before it turns to rain.

    • JohnD says:

      What has been your snow totals where you are—throughout this event? Must be pretty impressive. Hopefully we’ll get a PNW reload by month end—including Stateside—although I get the impression that no one is holding their breath!

      • Roland Derksen says:

        By “this event’ do you mean from Christmas eve onward? If so, i’ve measured (by an estimate) 14 inches to the 31st. We had another couple of inches today. it’s quite variable however- i’m down at an elevation of 366ft. ASL. If I were to go up just a few hundred feet (to 1,000 for example) , it would be at least twice those amounts. The mountains here just north of us are absolutely covered solid. There are warnings of avalanches being posted- even below the tree line. It’s really something!

        • JohnD says:

          Thanks. Yeah entire event. The geography, multifaceted climate features, overall regional complexities—AND visual ambience all contribute in the PNW to it being such an incredibly awesome region!
          I’m a hiker too.

    • Diana F. says:

      Hey Roland!
      I am envious of the continued snow action at your place!

      And may I ask a favor of you!?
      If you could include your location in your posts, it would be so very helpful.
      As I’ve gotten older–
      I can’t even remember what I had for dinner last weekend lol!
      Ain’t NO WAY I can remember where Roland Derksen lives,
      even if he’s told me a time or two over the years!
      And hearing what your weather is doing loses a bit of its punch,
      if I can’t correlate it to a specific location in our forecast area, ya know?

      AND I AM ASKING THE SAME OF EVERYONE!
      Please share your location!
      THANK YOU!
      #Happy2022!
      #FeelsWeirdToWrite2022!

      • Roland Derksen says:

        Okay, Diane- i thought everyone here knew I was from BC, but I don’t mind sharing my address with someone one more time; I live in Vancouver, BC on the east side of the city at Lincoln Street (almost in Burnaby). i hope that’s enough. Anyway, yes- continued snow action. We had more yesterday than expected, and a big amount coming tonight as well. This winter probably won’t have near a record amount (like 1970-71) but it’s one of the snowier ones we’ve had for the past 2 decades.

  8. W7ENK says:

    7:51am — our latest sunrise.

    And with that, the “Dark Days” are now over. Sunrise now begins its slow journey back toward Midnight, marching farther to the North each morning until mid June.

  9. Mountain Man says:

    Just a little story: It’s great that what was advertised as the (“big”) thaw can’t thaw anything or at least not everything above 500-700 feet here around here. There’s still ice stuck to the roads, they keep trying to plow off at 700+ ft, it’s like several miles of icy speed bumps. Then Up here at 1400 feet, we got all of 12 hours of rain making a sloppy slimy mess, then just wet snow again and now more snow again. For the first time, I can’t make it up my driveway which is pretty long, something about it staying right between 32 and 33 makes for the most impassable snow, especially with it layering with the ice layer at the bottom and fresh wet snow on top is the worst. Had to haul all the groceries up the last big hill from the 4×4 with big luggy snow tires, it wouldn’t go any further, it sucked, we put them on the sled lol. Ahhh life as a Mountain Man! Even worse, I forgot to throw my boots in the truck early this morning!
    Well, crazy Columbia River Gorge, crazy passes, pretty crazy here in the foothills, but enjoy the wet roads if you’re in the lowlands, it’s fun up here, but it’s not “all” fun up here!

    • West Linn 200 says:

      That actually sounds like a lot of fun to be honest. I’m not sure I can handle that much snow for too long but a nice week of hiking through the powder just to get some groceries brings out character in a person lol

      • Mountain Man says:

        I suppose you’re right WL 200. You know, I have spent a long time in the mountains, but I had to drive all the way to Sandy and back today, makes me both appreciate what I have and what others have. I had a bulldozer for 12 years living in the central Gorge at almost the same elevation, could plow my road when it gets deep, I’d appreciate if I hadn’t sold that a few years ago earlier tonight!

  10. Currently 35.3, bottomed out at 32.8 at 5:05 PM.

  11. Evan -- Cedar Mill says:

    On 18z GFS 850mb temps are way above freezing for 10 days straight starting on the 9th. Awful.

  12. Ken in Wood Village says:

    Just saw that ODOT closed HWY 26 at Rhododendron over Mt. Hood. Driving conditions are really bad 😲😳

  13. Evan -- Cedar Mill says:

    Coast range at 250 ft got a quick bit of snowat 32.5F based road cams on trip check.

  14. Evan -- Cedar Mill says:

    Rain snow mix here. Likely all snow in west hills.

    • W7ENK says:

      What’s your elevation?

      I’m at 155′ in Milwaukie, and that last heavy shower that came through about an hour and a half ago transitioned to a 50/50 mix just as precip ended.

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