Snow Possibilities For Tonight & Early Next Week

Some of us in the metro area will see our first snow of 2018 tonight.  It’ll happen under the cover of darkness though.  Most of us will be sleeping peacefully through the white stuff and wake up to cool rain showers Wednesday morning.

So what’s up with this possible “surprise snow”?  A weak system is approaching the Pacific Northwest this evening.  Obviously it’s too warm to snow right now, and I DO NOT expect freezing overnight.  BUT, we have a very dry airmass over us.  When the air is this dry, temperatures drop quickly.  Evaporating precipitation removes heat from the air; it’s called evaporational cooling.  Model soundings and cross-sections show that cooling and generate snow in some areas.  Take a look at our RPM forecast at 2am:

It goes for at least a dusting above 500 feet or so around Cornelius Pass and north, plus much of Clark County.  Also the foothills east of Happy Valley, Gresham, and Oregon City could see at least a dusting.  So keep in mind many of these areas would wake up to some white covering the ground, but again, I think it won’t affect your AM commute unless you live up above 1,000′ in those areas. The WRF-GFS from UW shows a similar setup with those same areas getting some snow overnight.

After 3-4am a stronger onshore flow has kicked in west of the Cascades lifting the sticking snow level up around 2,000 feet or above.

Let’s move on to our next threat of lowland snow…that would be Sunday.


  1. There is no sign of a widespread snow event in the lowlands through at least Sunday/Monday next week
  2. But snow showers (even to the lowest elevations) are possible at any time from late Sunday through Monday
  3. Don’t alter any of your plans for Sunday-Tuesday next week for now.  This could easily end up being a “dusting on the barkdust” sort of event for many of us.
  4. The coldest airmass we’ve seen since Christmas moves into northern Oregon and southern Washington Sunday night and Monday

Models are in great agreement that we’ll see a cold upper-level trough digging south out of Western Canada Saturday & Sunday.  Initially that means lots of cold showers and mountain snow…that’s through Sunday morning/midday.  During this time we’ll have strong onshore flow (southwest wind) which will keep snow levels way up around 1,500′ or higher.  So there is little chance for low-elevation snow through at least Sunday morning/midday.  850mb temps are a little too warm as well, ranging from -3 on Saturday to -6 or so midday Sunday.  Typically this time of year you want to see at least -6 for low elevation snow at night, and -7 to -8 to see it during the daytime.

By Sunday evening and then continuing through at least Tuesday, it appears the airmass over NW Oregon and SW Washington will be cold enough to support the possibility of snow.  850mb temperatures drop to around -8 to -9 on both the GFS/ECMWF.  The operational ECMWF was even a bit colder, although its ensembles are more reasonable.  That said, the ECMWF model totally dries us out Sunday night and doesn’t really generate any lowland snow.

The GFS is similar, with very little at the lowest elevations.  This is because there just isn’t all that much moisture.  That GFS only produces 0.15″ precipitation over us from Sunday afternoon through Monday.  So moisture availability appears to be the main issue if you are looking for snow days either Monday or Tuesday.  That’s because the upper-level ridge is so close to us…the systems coming down from the north & northwest are typically quite dry.

Just beyond our 7 Day forecast, the ECMWF model shows a wave of moisture moving inland next Tuesday evening and Wednesday.  There is no cold Gorge wind so the flow quickly turns onshore; warming us up well above freezing by Wednesday.    So taken at face value, there is no obvious “great setup for snow” in the lowlands the next 7-8 days…just a very cool period beginning Sunday.

A series of these cool/cold systems will drop down over the Northwest beyond next Tuesday…we’re into a cool pattern the rest of the month!

I’ll be keeping a close eye on things of course the next few days.  There are always last-minute twists and turns in these marginal snow situations.

Chief Meteorologist Mark Nelsen


55 Responses to Snow Possibilities For Tonight & Early Next Week

  1. Lee Wilson says:

    We are getting very high winds, How could you miss this Mark! HOW!

  2. Mountain Man says:

    6 inches at 1200 ft near Skamania. That was a lot more then I expected!

  3. W7ENK says:

    Woke up to the rain coming down at a decent clip at 2:30a in Milwaukie. Took a peek outside at the street lights, looking for snowflakes mixing in. I think you all know what I’m going to say next, so I’ll just leave it at that…

    35 degrees for an overnight low.

  4. GTS1Kft says:

    1″ on the deck and railings – pretty much all white except the areas under the trees…

  5. Joshua Downtown PDX says:

    Great job forecasting, Mark. Overall, you were on the money.

  6. Excellent forecast, Mark. Woke up to a dusting, maybe 1/2″ if you’re generous or prone to exaggeration, in Vancouver, WA. Fat rain falling on the drive to work in Camas.

  7. alohabb says:

    Snow/rain in Aloha.

  8. Ken in Wood Village says:

    Just had a trace here. I see some more moisture coming over the West Hills so I’ll see what happens out here!!

    I like the 00Z EURO model. Gives us some nice cold air Sunday and beyond. 🙂

  9. JERAT416 says:

    Trace of snow on cars, grass , and barkdust this morning. 34 and light rain at my house on Bull Mtn at 630 ft

  10. Max in Fairview says:

    Changed to all snow for a while and sticking to cars.

  11. Tyler Mode in Battle Ground says:

    Just over 1/2″ here in Battle Ground. Temp is 33.

  12. West Linn 500' says:

    Light amounts of wet snow, or perhaps snowy rain

  13. Longview 400 ft says:

    Have some wet snow flakes with the rain here.
    38.8 currently

  14. W7ENK says:

    FWIW: What started out as a cold rain has turned into sticking snow in the Puget Sound Basin down to some pretty low elevations this evening…


  15. Paul D says:

    I don’t care whether or not it snows, I’m just glad to FINALLY see some normal and BELOW normal temperatures!! Woot!!!

  16. Anonymous says:

    The warm air is coming in 😪😪😪. Temperature went from 30 to 33

  17. Anonymous says:

    Winter weather advisory for foothills

  18. Anonymous says:

    I pull for lowland snow more than most, but this just feels ‘too little too late’ — fill up the mountains and lets get on with Spring, shall we?

  19. W7ENK says:

    Not gonna happen.

    I’ll believe it when I see it.

    Did I leave anything out??

    • Boring Rain says:

      Eh, 33 degrees would probabaly be snow in this situation. So maybe 35? Otherwise, well done. Down to 31 here.

    • Mark says:

      Boromir! (I think from LoTRs) = perfect. LOL!

      • W7ENK says:


        That’s Ned Stark from ‘Game of Thrones.’

        “Winter is coming.” His family’s famous tagline.

      • Sprayandpay says:

        Boromir was A LOT better in books vs movie. In books he was a very likable character and had good moral values he stuck by like crazy glue.

    • Jason Hougak says:

      Yeah, tired of seeing this posted over and over again!

    • Jake in Gresham says:

      A few months back I purchased an Ambient Weather WS-2902. It has this fancy display and one of the indications shows if it’s cloudy outside or raining. Right now it has the indicator for clouds and precipitation.

      Conclusion: I purchased a torture device.

      • Ken in Wood Village says:

        LOL, thank you for the info Jake. I’m just thinking of it for now. If anything, I should have bought something before winter started…hehe. I have plenty of time to buy something before next winter…lol

        • Jake in Gresham says:

          You have no idea how peeved I am right now! The darn thing has “professional weather station” in its title. And it has this indicator like other cheap weather stations. I’m really thinking of returning it. Windchill, UV index or not! Crap. No focus for the charts.

        • Ken in Wood Village says:

          Hmmm, I guess I won’t get that one then. Sorry for what you have gone through. If I where you, I would return it and see about getting something different.

    • Sprayandpay says:

      The change it had to come. Knew it all along.

  20. Jason Hougak says:

    Down to 30F here in the foothills of the Cascades at 1300′
    Bring on the snow!

  21. Ken in Wood Village says:

    I don’t have a outdoor thermometer so I look at NWS for Troutdale and I’m a little impressed with how the temp has fallen in the last hour. It was 50F around 6pm (maybe a little lower) but at 7:20pm it’s 37F with a dewpoint of 25F now. I haven’t looked outside for about an hour but last time the skies were clear. Troutdale is reporting fair skies so I’m assuming it’s the same here since I live about 3 miles from the airport. It will be interesting what happens tonight. 🙂

  22. Larry says:

    Gotta get out the wishtrain graphic this late in the season. I still think it’s too warm but you make some valid points. Guess we’ll see if 35° rain can turn white for a few minutes.

  23. Garrison - Christian says:

    Already 33 in Aumsville

  24. Philip says:

    Will Willamina Oregon see any specific snow falling

  25. Garrison - Aumsville says:

    Already 36F here in Aumsville at 375FT. Could we stay at or below freezing when the precipation comes???

    What are you guys’ current temps and few points?

  26. MasterNate says:

    I guess my question would be, if we dry out and go all clear early next week, how low will the low temps go in the normally cooler outline areas?

  27. Ken in Wood Village says:

    First 🙂

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