Chilly week ahead, but tough to get REAL snow to lowlands this week

3pm Sunday…

Thanksgiving weekend is wrapping up and now it’s on to the last few days of November and then December. Right on cue, a colder airmass is arriving today with cold showers. I’ve seen a mix of hail/rain at home.

Snow hasn’t been too heavy in the Cascades so far, but intensity picks up a lot tonight through midday Monday. Cascades are the easy part of the forecast. Expect another 10-15″ at pass elevations (a bit more higher up) tonight through Monday. Add in a colder airmass and that means tomorrow morning you cold have 20+ miles of snow to drive through. That’s much tougher than just a few miles over the summits. Snow will stick down to around 1,000′ in the Cascade foothills tonight; I’m putting out my “snow board” for the season, anticipating a brief dusting here at home…maybe. This plus another 12-24″ Tuesday night through Thursday means ski areas should all be able to open this coming weekend with many feet on the ground!

Highlights for the lowlands

If you have a short attention span, or in a hurry, this is what I’m thinking over the next week or so…

1) Get used to lows/highs in the 30s/40s the next 7-10 days. Not really that cold, but these are mid-winter temps; a bit cooler than average for this time of year

2) There’s NO SIGN of an “arctic blast” west of the Cascades for at least the next week. No “pipe-busting” cold or anything colder than what we’ve seen so far this season. There’s also no sign of any significant cold east wind through the Gorge this week; typically that would help us get something frozen (snow or freezing rain). Not this week.

3) But, we have a few “close calls” with low elevation snow over the next week. Mainly late tonight, Tuesday evening/night (for some), and Wednesday night/Thursday AM. There’s a good chance that none of these produce measurable snow in the vast majority of the I-5 corridor from Clark county down to Eugene

4) The issue is that when it IS just barely cold enough for snow to stick to sea level this week, the precipitation is mainly gone. The heavier precipitation periods will be a bit “warmer”.

4) That also means that at this point I don’t see snow impacting your life Monday, Tuesday daytime, Wednesday, or Friday through Sunday in the lowest elevations. That could change, but it’s what I’m seeing right now

The Details

We are under the influence of a chilly northwest flow in the upper-atmosphere. A cold upper trough is passing through tonight, with 850mb temps down around -5 to -6 and 1000-500mb thicknesses around 520-521dm.

(KPTV)

Typically, to get snow in the lowest elevations, with onshore flow, we want to see -7 to -8 at 850mb and 520 or lower thickness. So at best the lower elevations with see snow mixed with rain overnight like we saw a few weeks ago…weak sauce. By the time it get’s quite cold (tomorrow evening and tomorrow night), the precipitation is all gone and we stay dry. I notice the freezing level bottoms out around 1,800′ tomorrow midday, so with relatively light showers early tomorrow, I wouldn’t expect sticking snow in the metro area below 1,000′…if it even gets that low.

Then Tuesday night and Wednesday another cold upper-level trough digs down from the north, but this one is headed farther west of us at first…Tuesday here:

(KPTV)

That means the really cold (arctic) air is dumping out over the Gulf of Alaska. It does spin up a nice bomb cyclone near the northern tip of Vancouver Island. Looks like a drop from 1012 to 978mb out there from Tuesday AM to Wednesday AM. But a surface low in that position pulls up a southerly wind over us = snow-killer in the lowlands. That said, as the precipitation starts Tuesday evening, it could easily start as snow but not stick out in Columbia county in Oregon and Cowlitz county in Washington. I’ll be watching that closely, but rarely has that pattern produced anything very interesting snow-wise in the metro area. So expect plenty of rain and big mountain snow during this time. Here’s the GRAF model’s snow forecast through Tuesday night. This sure doesn’t say “I’ll be sledding early this week in Portland”.

Blog images

One more way to look at it is the cross-section from the UW-WRF model. The zero line (32 degrees) is blue. Above that line it’s at/below freezing. I didn’t draw correctly on Tuesday, obviously we are above freezing most of that day. You can see the southerly wind (barb-looking things) pushing freezing level up to around 3,000′ later Tuesday night

By Thursday, that trough is STILL just barely moving onshore.

A lot of the energy has gone south us and into California. That delays the arrival of cooler air again and modifies the cold airmass offshore a bit further. At the surface an elongated band of rain/snow has become almost stationary over the West Coast Thursday

Another gray day with possibly a rain/snow mix in the lowlands, or just rain. Some models HAVE been implying we could get into a situation with heavy precipitation within the frontal boundary changes somewhere in Oregon over to all snow. I’ll be watching for that possibility closely; this model run says that may happen in SW Oregon; notice all the snow down there.

By Saturday, that trough is gone and another is swinging south; offshore like the Tuesday/Wednesday trough

You get the idea…much of the action is happening well west of us over the ocean. This spins up another wet frontal system for a solid period of cold rain sometime Friday through early Saturday, with showers to follow Sunday. 3-4 days ago models were keeping these troughs much closer to the coastline and bringing cold air down directly over us. Another way to see how they adjusted, a chat showing 6 hourly minimum temperatures out in time. Each horizontal line is one run of the ECMWF model. Notice the Thanksgiving morning run (12z 24 Nov) was showing very cold weather later this week with modified arctic air coming in from the north (upper part of circled area). Then in the 6 model runs since that time, ending with the latest, you see we’re back much closer to normal with a forecast for later this week. No arctic air moves south, but maybe some close calls with snow in the hills and mixed in the lowlands.

Maybe a better real world translation is: “3-4 days ago I was worried my wife would have issues getting to work in the early mornings this week. Now I’m not worried at all. Maybe an inch or so sometime in the next few days at 1,000′, but that’s about it”.

That’s it for now, I’ll be at work all week long!

43 Responses to Chilly week ahead, but tough to get REAL snow to lowlands this week

  1. Mountain Man says:

    Well it is still just cold enough for flakes, temp hasn’t gone up yet at all, but warmer air must have finally moved in above because I’ve changed to rain from big flakes over the last hour. I had 5 inches though today, 1.5″ yesterday and 1″ before midnight Sunday. Unfortunately it looks like I’ll be melting out until the next front but it was pretty while it lasted. I’m at 1400 feet in the foothills not far west from Mt Rainier if you wonder where I am…

  2. Ken in Wood Village says:

    Lmao, I love when they put this for precipitation 🤣🤣🤣

  3. Roland Derksen says:

    Snow started here late this morning. It’s actually been fairly light up til now, but there’s a pretty brisk east wind blowing it around.

  4. Ken in Wood Village says:

    The temperatures keep falling 🤔

  5. tim says:

    Pesky snow in Seattle now.

  6. Andrew says:

    Seems like everything is playing out exactly as forecasted this morning. I think people might be a bit caught off guard by this evening when amidst all the cold/snow talk we actually have a pretty nice and wet south wind event.

  7. Ken in Wood Village says:

    I was looking at the 06Z HRRR which goes out 48 hours. Close to the end of the run, it turns the precipitation over to snow in the Portland area. I know a lot can change between now and then but it’s something to watch and see if the HRRR shows it again 🤗❄️

  8. Jim says:

    Spokane down to 14 at 10pm. That’s why this week and next weekend are going to be real interesting to watch

  9. Andrew says:

    Trying to draw any conclusions from models beyond Friday is futile right now. So much dispersion in the ensemble members. it’s clearly a very dynamic situation with so much cold air near the region. Even though nine times out of ten these situations don’t produce sea level action, they are what makes this stuff fun – playing the waiting game and seeing if models come into some kind of favorable alignment!

  10. ocpaul says:

    Yeah, no snow and cold is great. Absolutely great.

  11. tim says:

    Winter weather advisory for Seattle, I’m still not expecting snow at sealevel it’s mainly above 500ft.

  12. X says:

    Even the legendary Nov 1955 from what I recall didn’t just come out of nowhere though it may seemed like it to many: Cold air advocation had built up unusually early points north and the mountains had a decent snowpack setup prior so it was only a matter of time before something gave way.

    Mountain snow pack seems to favor lingering cold air better then without the support.

    • Andrew says:

      I appreciate the observation. My concern would be that eventually the very cold air to our north will be displaced with warmer air, right? These air masses are constantly rotating and moving around. I
      know patterns can persist (as we saw with last winters death ridge) but it feels like wishful thinking to assume we’re just going to have arctic air camped out in lower canada for weeks. Perhaps i’m wrong but i tend to view all weather patterns as fairly transient in nature, which is why it’s so torturous having really cold air so close but fail to generate the right system to pull it in.

  13. X says:

    It feels like we all have to go back to basic weather school again as we all seem to forget it takes time for cold air advocation to build up then come south when conditions are favorable for the release. That appears to be what’s happening for the mid December cold wave. It will build up first to the north then the hammer will drop. .

    What it WON’T do is just happen spontaneously which is what the GFS seems to like to show a lot then for some reason everyone (but me) fires up the snow cannons only to be disappointed. I’ve seen enough Novembers to remember how this usually plays out and the rare exceptions all had cold air build up before the dam breaks.

  14. Longview 400 ft says:

    Snowing here at 41.4 degrees and dropping.
    Currently 38.7

    • X says:

      Must be low dewpoints? That can happen if the dew is low then both meet somewhere in the middle. I’ve also seen that many times. I call it ‘fake’ snow since it’s not a real source.

    • X says:

      But ‘dewpoint’ snow from a bit of easterly wind is always welcome IMBY regardless if it’s a fake or real source. It’s fun to watch that brief magical change.

    • Longview 400 ft says:

      Currently 37.6
      Still snowing.

      • X (Aumsville) says:

        What’s your dewpoint? Sun came out around noonish now it’s dark again.

      • Aumsville Oregon says:

        My comments aren’t getting thru sometimes. I hate this Mark shadowban crap just for asking a question about dewpoints. I don’t see anything even remotely offensive about dewpoints.

      • Longview 400 ft says:

        Currently sunny again, temp 39.7.
        Not sure what the dew point is.

        I went out to get milk, and looked to the north and saw dark gray sky. I decided to wait that out and watch.
        Started out as a hail shower then turned to snow. A real good snow shower for about 10 to 15 minutes.

  15. Roland Derksen says:

    We’re expecting snow here at Vancouver BC this week, but just how much depends on a number of variables. Where I am, it tends to snow more often than other parts of the city , as I’m at a higher elevation than most residents. But- as an experienced weather observer I have learned not to get my hopes up too much. There have been times where I was sure I’d see snow (and a lot of it) only to see it turn to rain in an hour or so!

    • X says:

      If you get low enough dewpoints from cold air nearby which I think is going to be the theme the next few weeks your likely to be golden for ‘dewpoint’ snow which comes fast then vanishes as fast. The brief transition though is very magical.

      It’s beautiful when that happens as it comes real fast and brief when overall 850mb conditions don’t support it.

  16. WEATHERDAN says:

    In the space of 24 hours weathermodels.com has had these forecasts for Salem on December 11th. Sunday November 28th AM it was a high of 21 and a low of 6. On their afternoon run it was a high of 59 and a low of 46. Today their forecast for December 11th for Salem is a high of 36 and a low of 25. What could possibly cause such radical changes in a space of 24 hours? The GFS meteogram was similar but not as radical. It reminds me of a past OMSI weather conference when Rod Hill finished his presentation by saying “will it be warm or will it be cold this Winter, we don’t know”. Peace.

  17. tim says:

    Impressive snow storm for Salem/Eugene Thursday into Friday. 4-6” looking good. Hopefully deep freeze next week with highs in the 20s

  18. tim says:

    Well that was fun all that talk about cold and snow and yet we won’t even see a flake at sealevel and after last December artic blast/snowstorm that’s fine by me, it’s not even winter yet so there’s still a chance will get some snow before spring.

    • X says:

      It’s usually too early for decent cold to support snow at the 850mb level this time of year but later towards Xmas is a different matter.

      We always play this stupid game minus last year which was actually nice that the mountains got dumped and we didn’t have to worry about us being marginal.

  19. Andrew says:

    Great analysis, Mark. Thanks. Bummer that this week petered out, but the proximity of cold air seems to stay with us for a bit so plenty of reason to keep monitoring the system paths.

    • X says:

      I always hated playing the ‘marginal’ snow game wondering if we will get phantom snow. I’d rather the mountains get dumped on first like last year though I wish it started in Mid November instead of all those AR events that lasted till about now.

  20. Mountain Man says:

    All white up here now at 1400 feet, maybe a half inch in the last hour when it started sticking. Yes Mountain Man is still here, I don’t comment that often. Hope you snow lovers in the lowlands get something soon! I got a feeling about what might happen late in the week and there’s definitely been lots of eye candy sprinkles in the models past that.

    • X says:

      Exactly it takes time for cold air to build. It doesn’t just ‘magically’ come out of nowhere. I always thought it was way too soon to fire the snow cannons on here or any weather forum.

  21. X says:

    (Almost) every stinking November they pull this BS.
    “There’s a chance of snow at 35F!” with almost zero Artic airmass support for it which is what you need to get the lower levels primed.

    You’d think people have learned by now to realize you need actual cold air either at or near us for there to be actual support for low snow below 1,000 feet.

    That cold air isn’t there and never was for most of these types of marginal events. The weather models generally rely on historical data for their forecasts and do their best to compute it but in the end it’s just a numbers game relying on certain conditions of the past:

    However their info is outdated so until it reflects our modern warming and other things we will continue to have a broken GFS no matter the resolution patches. It will always be internally broken.

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