A Busy Weather Week Ahead: Low Elevation Snow Update

10am Saturday…

I’ve been checking all the latest maps/models and meteorological goodies over my morning drink.  Doesn’t everyone else wake up on a Saturday morning and do that as well???

December-February is winter as far as meteorologists are concerned, and west of the Cascades just about all our winter weather (snow/ice/big storms) occurs in December/January most years.  Right on schedule, next week will be our first wintry week of the season with a:  1) strong cold front Sunday morning,  2) marginal snow event for the lowlands Monday, and 3) possibly a widespread snow/ice event in the metro area and (for sure) Gorge Thursday.  Beyond that we’ll most likely warm up again.

MONDAY SNOW

A strong cold front will pass through the region very early Sunday morning.  In fact by the time you wake up it’ll already be down around 40 degrees and there may even be snow mixed in up in the hills, but no sticking below 1,500′.  Then at midday the rain stops and skies break open to sunshine.  Sunday afternoon looks great!  Partly cloudy and mainly/all dry with light wind.  Last chance to hang your Christmas lights in dry and comfortable weather for a while.  Late Sunday night and the first part of Monday is when it gets real interesting.  A “cluster” of showers moves inland, right after skies have cleared overnight.  At this point it’s marginally cold enough to get sticking snow down to the lowest elevations west of the Cascades.  But if we get a burst of heavy enough showers, we could easily get some of that snow to stick down here at the valley floor.  Very tough call in these situations.  If you want it to snow, we have the overnight cooling to help us, yet we also have a mixing southerly wind that tends to keep the snow level off the valley floor.  Models are in very good agreement showing .15″ to .30″ precipitation during this time.  That would be enough for 1-3″ snow accumulation if it all made it to the ground.  That’s very unlikely in the lowest elevations.  But I’m not paid to just see-saw back and forth over what may or may not happen…this is what I think is most likely…

SUNDAY-MONDAY HIGHLIGHTS

  • Rainy start Sunday, then dry and partly cloudy, no sticking snow below 1,500
  • During Monday AM commute, EVERYONE WILL SEE SNOW IN THE AIR as snow showers arrive before sunrise
  • If you live ABOVE 1,000′, expect 1-2″ snow on the ground by mid-morning
  • If you live in the higher hills around town (West Hills/Mt. Scott/Sylvan) near 1,000′, expect a trace to 1″
  • At the surface (where most of us live) a dusting is possible, maybe even up to 1″ on the lawns/barkdust
  • I DON’T EXPECT MAJOR IMPACTS TO THE A.M. COMMUTE ON HIGHWAYS/FREEWAYS, but probably very slow as we all gawk at the snow
  • SOME SNOW WILL GET ON ROADS HIGHER UP IN HILLS (for sure above 1,000′)
  • Monday afternoon commute will be uneventful with temperatures in the upper 30s and scattered light showers

So obviously we’re all going to really excited about seeing the first snow of the season, but a bunch of snow accumulating on metro highways is pretty unlikely in this pattern.

Note the different model snow forecasts.  It’s important not to read these too “literally” because the terrain of the model may not match the actual terrain.  For example, notice on all three there is significant snow on I-5 between Longview and Woodland.  That’s because the narrow gap the Columbia River cuts through the hills isn’t resolved on this resolution model, so it just thinks the hills continue right across the low areas.  The West Hills, Chehalem Mtn, and south Salem hills show up nicely on the WRF-GFS (middle image) though.  The same thing happens in the Gorge.  Most models (unless they have less than 5 km resolution) just see the Gorge as a low mountain pass.  Thus Cascade Locks may be seen as a 2,000′ pass instead of at sea level, similar setup for Hood River too.

ecm_snow_10pm-10ammon

mondaypm_snow

rpm_snow_12z

Whatever happens the first half of Monday, by afternoon it’ll just be snow/rain showers in the lowest elevations as temperatures “warm” up to 40 or so.

We might have a leftover flurry Monday night or Tuesday, but for now it looks like far less moisture available.  Beyond that time we go into dry and cold for a couple of days.

LATE WEEK SNOW/ICE

On Wednesday a cold east wind starts blowing out of the Gorge and that sets us up for what we call a “transition event”.  Here in the lowlands of Western Oregon and SW Washington there are two ways we get snow (generally).  The first is the showers flowing onshore like Monday which involves no cold/dry continental air coming in from the east.  On Monday the lower elevations of the Gorge have the same weather we do in the western valleys.   This first situation rarely provides much snow and it’s always a real marginal situation.  I don’t think I’ve ever seen it below 30-32 degrees in this pattern.

The 2nd way we get snow is when cold air is in place (often via cold air moving in from the Gorge) and then moisture returns from the west overhead.  This typically is at the end of a cold period.  That pattern is how we get our big/significant snow/ice storms.  That setup is coming either Wednesday night or Thursday.  And this far out details are very much subject to change.

By Wednesday night a very strong east wind will likely be blowing through the Gorge and out into the metro area.  10-12 millibars easterly gradient = brrrr!  That’s the usual gusts to 100 at Vista House and 70 mph in most of the usual windy settlements at the west end.  At the same time a warmer front is approaching.  Check out the WRF-GFS map for late Wednesday night and you can see thick cold air dammed up in the Eastern Gorge, pouring out the west end:

slp-120-0000

I’ve been around this block a few times…that setup, along with a bunch of precipitation arriving, screams SNOW STORM IN THE GORGE and/or ICE STORM FOR PART OF THE GORGE.  Or most likely a combo.  If the air is cold enough, this could be a snow/ice event in the metro area too.  We won’t really know the details of that until Wednesday when the colder air is in place.

LATE WEEK HIGHLIGHTS

  • Some sort of significant snow/ice storm is likely in the Gorge either late Wednesday night or Thursday
  • It MAY be cold enough for snow and/or freezing rain in at least parts of the metro area too
  • Whatever happens will most likely occur overnight Wednesday night into Thursday

Stay tuned!

Tonight I’ll be out in Seaside for the Providence Festival of Trees.  It’s a great event to raise money for the Providence Seaside Hospital Foundation.  Stop by and say hello if you see me.  Just don’t shake my hand…I think I have some sort of cold coming on…poor timing…

Chief Meteorologist Mark Nelsen

 

 

 

 

 

60 Responses to A Busy Weather Week Ahead: Low Elevation Snow Update

  1. Lee Wilson says:

    Snooping Lives! Not sure how or why or what happened..bUT our snoopy blow up.finally inflated it’s self this morning.

    Ok, want is up with all that snow passing us by? TOLEDO Washington and Castle Rock seem to be 8n some kind of wierd warm area..

    There is snow to the east and to the west…but we’re like this little island of no snow.

    And that was an impressive snow Cloud that passed us by on the radar.
    We’re at a whopp8ng 36.

  2. Lee Wilson says:

    Reporting in .
    We have Ice forming.
    Were at 34, we had rain then we had a few snow flakes.
    Then it started to Freeze.
    https://www.youtube.com/edit?o=U&video_id=t70F-kMLxEc

  3. Scooter says:

    Amazing amount of “bro trucks” with their diesel smoke and noise driving out for Christmas trees throughout the countryside today, not to mention “trophy wives'” peering out of the passenger seat with their ‘happy place’ look on their pretty little faces. Bless you all & Enjoy the Holiday Season while they last.

  4. Washougal1100ft says:

    It’s snowing 34 out! Starting to get white out!

  5. High Desert Mat says:

    Lightning strike east of pdx. That would be thunder snow. I’m thinking of Jim Cantore about now.

    Mark, we need an update from you. For tomorrow since it looks like things may be interesting there by morning and the high possibility of a metro snow or zr event overnight Wednesday into Thursday. That is one juicy system.

  6. Jason Hougak says:

    Nice graupel shower just came through and quickly dusted the ground.

  7. Roland Derksen says:

    Clear skies this morning with a fresh SW wind- beautiful! Saw the snow laden mountains finally. Clouds are beginning to increase this afternoon, now… snow tonight?? I hope.

  8. Diana F. says:

    Now THIS is a week of interesting Weather!!! Finally!!! wooohoooo!!
    Although….there’s only ONE snowflake dancing around my page right now. Is that a bad sign??

  9. Washougal1100ft says:

    NWS – significant snow and ice storm possibly later in the week? Now that won’t happen thanks NWS!

  10. NWS is now forecasting some Fraser outflow on Tuesday. Nothing dramatic, temps mostly in the thirties, not the teens or twenties, and more breezy than windy. Precip forecast is settling down to a dusting of snow or just flakes in the air for me. An arctic blast an epic snow this will not be, but hopefully a preview of a more dramatic event to come.

  11. Sapo says:

    No matter what happens, this has already been more interesting than a lot of our winters have been at this point in the past. Models long-term look decent too so this might not be our only shot. I’m hoping for snow Thursday though…freezing rain sucks.

    • Paul D says:

      No kidding! The past couple of winters don’t even deserve the term “winter” associated with them.

  12. Grazman says:

    Winter weather advisory has just been issued for Portland

  13. cgavic says:

    cliff gavic in sandy at 1k ft.m 41 degs, rain.

    rhodadenderon has 4″ snow, 32 degs., at 1500 ft.

    a friend of mine living up above Estacada at 2k ft. has 12″+ and snowing heavily.

  14. Jason Hougak says:

    It’s changed over to snow up here in Cascade foothills. Back end of precipitation so for now it’s just a tease.

  15. GTS1K' says:

    Temp started dropping here at about 5AM. Steady at 42.5 ’til then – 38.7 now…

    • Jason Hougak says:

      Where you located at?
      Same here down to 37F, heavy precipitation here is driving down that snow level and it is beginning to mix some wet snow. Back edge of precipitation heading across NW Oregon turning to showers. The water vapor shows a nice low pressure spinning down from SE Alaska.

      Anybody seen the 06Z GFS…😳
      Cold building into BC and arctic air filter down into PNW. Over water trajectory with a lot of precipitation. The snow accumulation loop is impressive… redux Dec. 2008 if this pan out.

    • GTS1K' says:

      Skyline & Germantown – no precip since about 6:30 but radar looks promising if the coast range isn’t too hungry.

  16. Reston says:

    Hey Mark,
    Any chance you would be amenable to including a blurb about road conditions for cyclists?
    Specifically re likelihood of ice accumulation.
    I really trust in the reliability of your forecasts, it would be awesome if I could get more specificity that affects my bikeability during these crap inclement days, out here in NW Industrial PDX it can be pretty unpredictable
    A day out of the saddle is a dark one, indeed.
    Thanks, man!!

  17. Bob says:

    Bob the weather cat says it going to be a snowy week.

  18. Windsday says:

    Here is the Eugene Register Guard Google News Archive image of Dec 4th 1949 just before the famous cold. I hope it shows up as a hyperlink you can click on.

    https://news.google.com/newspapers?nid=4pF9x-cDGsoC&dat=19491204&printsec=frontpage&hl=en

    To see the rest of the newspaper articles click on Browse this Paper and click view on dates. Always use Open Link on New Tab if you wish to view another date or otherwise you will lose your spot.

    As for the article:

    Scroll to the bottom to
    Ah California! Her Weather Has Moved North:

    Here I type the first paragraph of said article which goes on to mention after a false start in October most of the fall was very sunny with warm south winds:

    Oregon can claim some of California’s weather of late. for certainly what the weatherman has been sending is unusual.

  19. JohnD says:

    Just got back from a day visiting an 89 year old family friend down in Albany. We live in inner SWPDX off Corbett (Lair Hill area.). We joke because “Lair Hill” is the name of a historical pioneer and not a “hill” at all per se–although the “crest” of Corbett and Bancroft I’m thinking must be around 300′–judging from the tops of the South Waterfront buildings nearby.

    In any event, I just remarked to my wife that the 46.7′ currently reading on our thermometer “may” be the highest that we see until next Friday–if then! We’ll see–right!?

    • Windsday says:

      Just like in the article I posted which 1949 was a MUCH warmer fall then normal skewing averages.

  20. Paul D says:

    Let me summarize: over the next seven days we will have weather! I am 100% certain of that!

  21. bjvanwash says:

    Mark, or anyone else, do you have a link for that WRF-GFS(925mb temp and 10m wind) picture you posted? I see those on here quite often but haven’t been able to find where it’s from. Thanks.

  22. Timmy Supercell (Klamath Falls, OR) says:

    It’s snowing on the blog.. Now it’s not gonna happen. 😛

  23. W7ENK says:

    33 DEGREE RAIN ADVISORY
    NATIONAL WEATHER SERVICE PORTLAND OR
    154 PM PST SAT DEC 3 2016

    https://inws.ncep.noaa.gov/a/a.php?i=7381898

  24. Steve says:

    What was your morning drink?

  25. Boydo3 N. Albany says:

    THIS JUST IN…. 12Z operational ECMWF has an arctic front sagging down in just 9-10 days!

  26. Roland Derksen says:

    Locally the weather office here issued a “Special weather statement ‘ for Sunday night into Monday, but they’re still hedging as to what ‘s exactly going to happen. I’m hopeful, but still doubting about how much snow we’ll see.

  27. Anonymous says:

    You mean have a morning drink?

  28. Sandi (Wilsonville) says:

    I hope you feel better soon!

  29. W7ENK says:

    Prepare for strong to severe disappointment…

  30. Jason Hougak says:

    What happened to your blog last night? It kept saying an error had occurred and the website was reloading. When it reloaded then you couldn’t type anything. Do you do that to limit comments😆

    Also Mark do can you have a box to save our name and email. Some of us are having to enter it every time which is a PITA!

  31. Ron says:

    But sadly, no snow at the beach.

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