Snow Outlook

I happened to be scheduled to work this weekend…how convenient in this case.

So is it going to snow in the city of Portland?  I would be surprised if the ground doesn’t at least get coated white either tomorrow evening or Monday afternoon/evening.  Will we get 4″ or more?  That seems very unlikely, but 2″ sure is within the realm of possibilites.

It’s getting cold out there tonight with clearing skies and drier dewpoints working down from the north and east.  Tonight should be the coldest so far this season (finally a frost at PDX!) for most of us.

I’m amazed at how much information we have nowadays and how detailed it can be.  When I started in this business around 1991, a cold upper-level trough and associated arctic airmass would plunge south, you could generally just say we’ll see somewhere between a trace and 2″ of snow within 12 hours of the frontal passage, and then it would get cold.  But look at today’s (and tonight’s) mesoscale modeling.  Our RPM, the WRF-GFS, and to a lesser extent the NAM-MM5 from the UW, all show two separate precipitation espisodes the next 48 hours.

The first is a burst of showers around sunset tomorrow as a weak surface low slides overhead and east towards Pendleton.  Larger and coarser modeling wouldn’t even be able to see this in the past.  The 2nd is a slightly stronger low or elongated low that slides by Monday afternoon. 

I feel a bit better about snow compared to last night at this time for these reasons:

1. Tomorrow’s burst of showers around sunset is just that…around sunset and beyond…good timing with a marginally cold-enough atmosphere for lowland snow.  Dark = cooler = good.

2. Wind is calm or light northwest both tomorrow and Monday afternoon…that’s always good to allow snow to fall a bit lower.  No south wind to mess things up.

3. Models (the last two mesoscale runs) have been steadily moving the Monday afternoon precipitation a bit farther north.

So here’s my forecast I’ll use at 10pm:


-Trace to 1″ possible tomorrow evening around sunset and just beyond.  Best bet for that 1″ would be on the hills and eastside (Gresham, Camas, Sandy, Battleground, etc…).  If the precipitation is heavy enough, it could be everywhere.  If we only get light showers; forget about the lowest elevations.

-1-2″ possible Monday afternoon/evening, even better chance south into Salem and Eugene. This is the one that could really make a mess.  If indeed snow DOES start to fall at mid-afternoon, roads are wet/slushy and then begin freezing up???  Well…I just keep thinking of December 29th, 2009.

Forget about the 300′, 500′, 750′ elevation distinctions…especially with showery precipitation!  That drives me nuts.  One place could get sticking snow to sea level (under a heavier shower), and another spot at 1,000′ might just get a mix under a light shower for no accumulation.

Chief Meteorologist Mark Nelsen

264 Responses to Snow Outlook

  1. Rachel says:

    I wonder about those years that we got snow in November. Were the winters those years more snowy than usual? Just wanted to know? I’m hoping for a winter packed with snow 🙂

    Rachel from Hillsboro

  2. jeri says:

    as of 2:33pm Sunday November 21st, it is snowing REALLY HARD in Vancouver/Orchards. It is sticking and accumulating very quickly – it is into the second hour of steady snowfall – very pretty!!

  3. jory (Sandy) says:

    Are there issues with the blog? There seems to be a gap from 11:05 to 1:17 with no posts, even though there is moisture coming in.

  4. jory (Sandy) says:

    Snowing hard in Sandy! 34.8 degrees.

  5. Timmy - scappoose says:

    Headed north on hwy 30, snowing in st helens, deer island at the lowest levels. Big wet flakes!

  6. J-Kelso says:

    35.6 still. Looks like some precip coming my way, hope it’s snow. 🙂

  7. fishinbeaverguy says:

    Wind out of the South at about 2-3mph, lets hope that doesn’t last long. Jumped the temp from 33 to 35 in a few of minutes.

  8. RobWaltemate says:

    Rain drops getting bigger here N of Long Beach. Temp 36.6

  9. Rob "Wrath" S.E. Portland says:

    As of 10 AM

    Pressure Gradients
    BLI-YWL: -9.3mb | 0.2mb Decrease
    OMK-YKA: -7.2mb | 0.3mb Decrease
    *A -negative reading = Offshore/Northerly flow. A +positive reading = Onshore/Southerly Flow.
    BLI-SEA: +1.0mb | 0.3mb Increase
    SEA-OLM: +0.3mb | 0.3mb Increase
    OLM-PDX: -0.8mb | 0.6mb Increase
    PDX-EUG: -1.0mb | 0.2mb Decrease
    *A -negative reading = Southerly flow. A +positive reading = Northerly flow.
    PDX-DLS: +0.7mb | 0.6mb Increase
    TTD-DLS: +0.3mb | 0.3mb Decrease
    OTH-GEG: +4.6mb | 0.9mb Increase
    *A -negative reading = Offshore/easterly flow. A+positive reading = Onshore/westerly flow.

  10. Jeremy says:

    SLE – Light south wind 5-10. 37f slowly dropping, clouding up. 26f this morning. Dew point way too high.

  11. RobWaltemate says:

    Just started to rain here 3 N of Long Beach

    • RobWaltemate says:

      Should also have said it is 36 and the wind here at my house says SE, but the clouds say NW.

    • RobWaltemate says:

      I went outside and the drops look small and close together, so to me, they look like they might have been snow further up? Maybe wishful thinking too. Sky is getting darker. The could cover here looks like Stratus.

    • Ryan (Walnut Grove) says:

      Set the radar under the rain/snow setting to “show” and it will change the resolution as well as indicate type of precip.

      I would guess a mix or rain if any of that hits us. Unfortunately it is moving west to east so the coast range will probably gobble it all up.

    • Rob "Wrath" S.E. Portland says:

      Honestly it’s going to be close, but right now I say no.. I don’t see temps cold enough and DP’s aren’t low enough either. We’ll see…..

    • Boydo3 500' North Albany says:

      Man, that blob is really moving in a hurry down the coast. I see it’s pretty much all snow in WA.

    • camas mom says:

      Going to pit batteries in my machine so i can give temp updates. Praying for moisture!

  12. cromer says:

    Rob, Insania in Felida wants to know what her chances for snow are this week. Thanks

    • Ryan (Walnut Grove) says:

      I’m not Rob but I would say the chances for everyone to see a little white stuff are pretty good.

      The key is getting underneath a shower. I would guess a few folks see nothing or just a few flakes. But, if someone gets a good shower, they could see an inch or two.

  13. …25.3 for a low; just popped above freezing,32.3 dp29.5….

  14. No Snow says:

    Sorry, snow will be only 200 feet and above! Everyone else down the street won’t get any.

  15. Rob "Wrath" S.E. Portland says:

    12Z Canadian

  16. stevied (North Portland) says:

    NWS 8:50am discussion for PDX pretty much unchanged.


  17. Rich says:

    Prune Hill, Camas.
    710′-freezing fog
    Temp: 31.1
    Gust: WNW 11Wind Chill: 26°F
    Humidity: 100%Dew Point: 31°F
    Avg Wind: 4 SSE
    Pressure: 29.73″
    Rain/Month: 5.66″

  18. snodaze says:

    Thank you Chuck on Mt. Scott… I don’t feel so naked now…

  19. Rob "Wrath" S.E. Portland says:

    12Z GFS Extracted….

    PDX: 850mb -14c / 507 thickness
    TTD: 850mb -15c / 507 thickness
    DLS: 850mb -17c / 504 thickness
    PDT: 850mb -19c / 504 thickness
    GEG: 850mb -20c / 505 thickness
    OMK: 850mb -20c / 501 thickness
    BLI: 850mb -17c / 503 thickness
    SEA: 850mb -16c / 505 thickness
    OLM: 850mb -15c / 506 thickness
    SLE: 850mb -15c / 508 thickness
    EUG: 850mb -14c / 511 thickness
    YWL: 850mb -25c / 492 thickness
    YKA: 850mb -26c / 495 thickness

  20. RobWaltemate says:

    N of Long Beach
    34.1 DP 32 with cloud cover in all directions
    No wind at all since a big gust of 1 mph around 1 am
    My kids are starting to get excited (me too).

  21. Rob "Wrath" S.E. Portland says:

    12Z GFS Extracted

    PDX: 850mb -14c / 507 thickness
    TTD: 850mb -15c / 507 thickness
    DLS: 850mb -17c / 504 thickness
    PDT: 850mb -19c / 504 thickness
    GEG: 850mb -20c / 505 thickness
    OMK: 850mb -20c / 501 thickness
    BLI: 850mb -17c / 503 thickness
    SEA: 850mb -16c / 505 thickness
    OLM: 850mb -15c / 506 thickness
    SLE: 850mb -15c / 508 thickness
    EUG: 850mb -14c / 511 thickness
    YWL: 850mb -25c / 492 thickness
    YKA: 850mb -26c / 495 thickness

  22. wendy-silverlake,WA says:

    Temperature has risen to 35 degrees and the clouds are clearing out to blue skies here.

  23. Chuck on Mt Scott says:

    Fog just started being pushed in up here from the south. Temp up to 31 after a low of 28. East winds were blowing slightly a couple hours ago, now are gone.

  24. Cgavic sandy Oregon 1,100 ft says:

    28degs and sun/ frost/ice

  25. alohabb says:

    If we see any moisture at all tonight, even if its just a little rain, temps could dip below freezing in the westside and create a REAL mess tom. morning!

  26. Ryan (Walnut Grove) says:

    Nice cloud shield pushing over Vancouver. I’m guessiv this is associated with the cold air mass pushing south?

    • Rob "Wrath" S.E. Portland says:

      It’s the developing system/BC slider dropping south from Vancouver Island. Arctic boundary is near Kelso.

    • Ryan (Walnut Grove) says:

      Figured as much… I’m working on our corporate ERP turnover so I can’t watch the sat/radar/model data. It’s lame!

  27. Rob "Wrath" S.E. Portland says:

    From looking at 12Z GFS it looks like as the trough slides east a surface high is definitely over the Columbia Basin into Idaho for increasing east winds Thursday through Saturday… Trapping the low level cold over PDX.

  28. Longview - 400 ft says:

    Currently 32.4
    Low this morning 27.9
    Low cloud cover with sun breaks.
    Hoping for snow today!!!

  29. PaulB/Eugene says:

    NAM and WRF/GFS MM5 models not looking good this morning in terms of snow amounts for Willamette Valley…although areas around PDX may pick up more. It appeared that there could be some snow S of Olympia as well…wait and see…it will be cold (not as cold as it could have been if there were decent snow amounts)…I would be fortunate to get an inch down here in Eugene.

    • Rob "Wrath" S.E. Portland says:

      Also looks like the low developing may be/become a touch stronger the models show.

    • ShawninSalem says:

      what happened?

    • PaulB/Eugene says:

      Low not developing off the coast much at all..heads into central OR so that we do not have a period onshore flow above with surface flow from the N…in other words, for the entire time there is moisture there is onshore flow at surface. A repeat of Dec 2009 is possible with NO snow at the valley floor, although PDX will likely get some accumulations.

    • PaulB/Eugene says:

      Honestly we do not know what will happen for sure….the models could be wrong on this.

    • ShawninSalem says:

      What are the other models indicating? Is this scenario look most likely now? Its annoying. I was looking forward to some snow around here tomorrow.

    • Rob "Wrath" S.E. Portland says:

      Oh so you don’t see the low off Vancouver Island right now dropping south developing much? I see enhanced clouds and a defined twist… maybe just 1-3 mb strong is my thinking near 1002-1005mb.

  30. Rob "Wrath" S.E. Portland says:

    As of 8 AM

    Pressure Gradients
    BLI-YWL: -9.2mb | 0.3mb Increase
    OMK-YKA: -7.0mb | No Change
    *A -negative reading = Offshore/Northerly flow. A +positive reading = Onshore/Southerly Flow.
    BLI-SEA: +0.7mb | 0.2mb Increase
    SEA-OLM: +0.0mb | 0.4mb Decrease
    OLM-PDX: -0.0mb | 0.2mb Decrease
    PDX-EUG: -0.9mb | 0.4mb Increase
    *A -negative reading = Southerly flow. A +positive reading = Northerly flow.
    PDX-DLS: -0.0mb | No Change
    TTD-DLS: -0.2mb | 0.3mb Decrease
    OTH-GEG: +3.7mb | 1.3mb Increase
    *A -negative reading = Offshore/easterly flow. A+positive reading = Onshore/westerly flow.

    Recap – Fraser Outflow continues, but not strong. Surface flow between Seattle to Olympia is teetering on turning southerly due to the new system digging south off Vancouver Island. Surface flow from Portland to Eugene has turned light southerly and that is a concern of mine that might ruin snow chances in PDX later today due to a possible increasing southerly gradient ahead of the low sliding south towards us.

  31. Currently a very crisp 29.2°F and partly cloudy with no trace of any wind. Roofs and lawns are silver from the frost. . . Very pretty out. . . . .

  32. kcteach-Gresham says:

    Cloud cover here now. Putting a blanket over those freezing temps.

  33. snodaze says:

    Two questions:

    Anyone have a valid working wxlinks.html?

    Are the links your posting text wrapping? or are the links extending out into the ‘archive’ section on the right of the blog?

  34. Doppler Dave (NE PDX) says:

    Ground beginning to turn white up in Puyallap.

  35. Kirk (Sandpoint Idaho) says:

    Sandi – yep that was me!

    Funny story I met my old neighbor on this blog (Camas Mom). No kidding we both lived in new houses on 5 acres so we had not run into each other until after blogging on here. She ended up becoming great friends with my wife.

  36. stevied (North Portland) says:

    WRF-GFS also shows some light snow beginning Monday by about 11am/Noon.

  37. stevied (North Portland) says:

    WRF-GFS this am shows some LIGHT snow falling around PDX about 1 or 2pm today.

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