Snowy Afternoon & Evening Tuesday, But Only For Some In Lowlands

6pm Monday…

We have one more “close call” with snow late tomorrow afternoon & evening, then continued cool and wet through the first few days of February.  Tomorrow will be dry through early afternoon, with a gusty east wind picking up after noon.  Temperatures reach the lower 40s. Then a wet weather system moves inland the 2nd half of the day. I expect precipitation to start sometime right after noon in the Coast Range and central Willamette Valley, then spread north into the metro area around 4pm. That leads to…

TUESDAY AFTERNOON & EVENING HIGHLIGHTS

  • THE VAST MAJORITY OF THE METRO AREA & LOWLANDS WILL NOT SEE STICKING SNOW TOMORROW AFTERNOON
  • BUT EXPECT A SNOWY MESS THROUGH THE COAST RANGE LATE TOMORROW AFTERNOON & EVENING. Watch out if you are headed that way! At least 3″ of snow is likely over Wilson River and Sunset Summits. Possibly down into the Van Duzer corridor between Lincoln City and Willamina as well.
  • Where the precipitation is heavier (far west metro up against Coast Range) we see a decent chance for at least a dusting.  That’s anywhere west of Hillsboro or North Plains.  It’s possible Forest Grove, Banks, Chehalem Mtn. pick up more than a trace.  Timing is 4pm-10pm.
  • We think there won’t be enough precipitation and/or temperatures won’t be cold enough for sticking snow (or even in the air) for just about all other areas.
  • Whatever happens will be done by midnight, then it’s back to light showers for Wednesday with temperatures in the 40s

TECHNICAL INFO

Models are in better agreement this evening. The general idea is that dewpoints drop into the 20s by midday due to a mild downsloping easterly wind (heading toward low pressure offshore). Temperatures with good mixing move into the 41-45 degree range in the lowlands. Then as precipitation arrives, evaporative cooling drops everyone at least a few degrees.

Generally the highest resolution models, which have the best topography, are forecasting no snow in the lowest elevations over and east of I-5. That’s because temperatures don’t drop down close to freezing tomorrow afternoon. That’s partly due to a breezy easterly wind (keeping air stirred up) and/or very light precipitation in those areas. There is no cold airmass east of the Cascades heading our way; the Columbia River Gorge is not “in play” this time around.

But west of I-5? Specifically close to the Coast Range? Cool air piles up a bit more, wind is light, and precipitation is much heavier. That can drag snow all the way down to the valley floor. Sometimes I’ve called this the “Forest Grove Effect”. I first noticed it early in my career. It can be breezy & 36-40 degrees in Portland. Yet calm, snowing, & 32-33 degrees way out against the Coast Range. I think that’ll be the case 24 hours from now. At this moment the HRRR shows this best…I like the temperatures for 5pm as well.

But the GRAF and RPM also forecast no snow. The contour pictured here is the 18z GRAF; it did very well with yesterday’s “event”. By the way, the ECMWF is accumulating snow for us with temps above 35 degrees…unlikely.

The (usually) reliable WRF-GFS at 1.33km resolution can see all the hills. It says forget it for anyone east of I-5, even up at 1,000′ or higher! This event is about LOCATION, not so much ELEVATION.

Regardless what happens in the late afternoon through early evening, slightly warmer air overhead should change anything to mainly rain showers after 10pm. Although there won’t be much precipitation by that time anyway. I’m guessing PDX goes from 43 tomorrow afternoon, down to 37-39 at 5-7pm, then back up to 39-40 by late evening.

We’ll see how this all plays out!

Chief Meteorologist Mark Nelsen

39 Responses to Snowy Afternoon & Evening Tuesday, But Only For Some In Lowlands

  1. JERAT416 says:

    Conversational snow in Hillsboro now. Bark dust and grass slightly white

  2. Tanis Leach says:

    Reports are showing from my friends out in Corvallis that snow is sticking in spots there.

  3. Tanis Leach says:

    So, one of my weather stations broke, I’m pretty sure. Its reading -40°F. Thankfully I have a second (and that one is properly mounted, need to get it registered), mounted in the last month. The 36.5°F from the other is reasonable. Also, 70/30 snow/rain ratio in Sherwood behind the middle school, trending right now towards more snow.

  4. W7ENK says:

    YEAH, baby… Look at that DOME!

    In’nit beautiful?

  5. Anonymous says:

    Seeing snow in Netarts.

  6. Andrew says:

    Mark’s forecast appears to be playing out spot on so far. East wind picking up but no real cold with it. Temps already nearing 40 around town. Some evaporative cooling expected but dew points much warmer than EURO forecasted (Mark nailed this) meaning cooling will be limited. Hope the west side metro gets in on action later but we seem destined for a Sunday repeat here in Portland. Oh well. Still a few weeks of prime season left.

  7. Scott Reeves says:

    Albany is getting snow

  8. W7ENK says:

    Light snowfall starting to enter the Western side of the South and Central Willamette Valley, though it would appear that most if not all of it is evaporating before reaching the ground.

  9. Jason Hougak says:

    Perfect recipe, clear overnight 28F with snow over, clouded over quickly to minimize warming. Very excited to see how this unfolds.

  10. Grizzly Bear says:

    Beautiful & peaceful light snow falling all morning, such a contrast to what I read here.

    • Ken in Sheridan 330 feet says:

      Sounds great! Where are you, Grizzly Bear?

      • GTS1Kft says:

        “Grizzly Bear” (AKA Farmer Ted,and all his other sock puppets) is living in a single-wide with “Ted Stryker” in Kamiah, ID. Apparently he “moved on up” from the Estamacada suburbs to Nazi country where he’ll probably fit right in.

        p.s. his “farming” days are over since he’s on a 5575 sq. ft. lot crammed into a gated rabbit warren of shacks where the gate is to keep people (using the term loosely) in – not out.

        I mean this in the nicest possible way…..

  11. Joshua Lake Oswego says:

    The 12z NAM high-res is bullish for snow. 3” along the I-5 corridor from Salem to Portland. Trending up as you go west and quickly less to the east. The HRRR gives a chance to far western Clackamas County, but mainly Washington County. The higher-res GEM gives a little hope to. Central and western Columbia, Washington, Yamhill counties on down look to score.

    I see a trend towards the heavier precipitation edging eastward a bit more than previously forecasted. Things are looking a bit more favorable for the central and western metro area, but best to keep our expectations in check.

    • Joshua Lake Oswego says:

      The WRF-GFS gives a glimmer of hope for a dusting west of the Willamette. The GRAF says nada. RPM too. HRRR is backing off. Let’s face it, most of us in the metro area will be lucky to see chunky rain.

  12. Tanis Leach says:

    Copied from my FB: For those interested in snow tomorrow, I made a video detailing the 3 different scenarios in Portland (with a touch of rest of Valley and Central Oregon): https://youtu.be/EjkOSKQtrjY
    In short: Further west is best, though most of you won’t see much if any stick (in 2 of the scenarios).

    I caught a grammar error to late (already published). Can anyone find it?

    And W7, 35-42 and mainly rain is my Milwaukee (depending on location) forecast tomorrow night to localize it more. 38 for the dome.

    I’m still working on how to word these better so constructive criticism is appreciated (or even a jump off a cliff message, though I likely won’t do that). This is my first non-Dam weather short-term video, and I don’t feel as good as I should about it. I’m only up another 30 minutes before going to bed (8:30 am class tomorrow), so I didn’t have time to polish it.

  13. W7ENK says:

    Okay, so the Kiss of Death is one thing, but did they really have to go and kiss it a second time???

    JFC man!! 🤦🏼‍♂️😭

    https://inws.ncep.noaa.gov/a/a.php?i=53472134

  14. Jason Hougak says:

    About 1.5” of snow yesterday afternoon into the evening. Went to work and came home to still snow covered ground. First 24hr snow on the ground for the season. 3 meager snowfalls with around an inch for each but I’ll take what I can get. Praying for an epic February.

  15. Tanis Leach says:

    I’ve been off for a few days, though I’ve been watching this closely. I’ll probably record a video tonight detailing the scenarios (trying to keep it under 5 minutes, though may not) and my full thoughts, but to keep it shorter, here are a few of the model scenarios.

    12z Euro 10-90% ensembles by 12z Wednesday at selected locations:
    Portland: .35-1.31 inches (temps don’t fully support)
    Hillsboro: 1.41-2.92 inches (temps to support)
    Salem: .06-.74 inches (temps don’t support)

    WRF GFS:
    Portland: Junk-.3 inches (depending on <200 ft location)
    Tualatin Valley: .5-1.5 inches, more on back of coast range.
    McMinville: Junk-.5 inches
    Everywhere else <250 feet: Junk

    • W7ENK says:

      My forecast for tomorrow, coming from a native who grew up here through all of the 80s, 90s, 2000s, 2010s, and now solid into the 2020s — Jeezus I’m getting old…

      1/24/2021 redux.
      38 degree rain.
      BOOK IT!!

  16. lurkingsince’14 says:

    The SWS puts 5-8” up in the higher foothills this next round, let’s see if it actually pans out…

  17. Andrew says:

    I had no idea Banks and Forest Grove were such hotbeds for snow! Learn something new with every post.

    I’m barely paying attention to tomorrow. Turning focus to longer term when GFS is trying to drop some more legitimate cold air our way in early February. Always chasing that cold air! haha

  18. Anonymous says:

    Mark you gave us your winter forecast a few months back looking forward whats your gut telling you chance for a major storm this February based on current models and trends ect I would love to see your one month outlook for portland

    • W7ENK says:

      Mark doesn’t play that game, he’s never stuck his neck out more than about 5 or 6 days. His forecasting style is extremely conservative, and he’s right to do so. He’s a PNW native, he knows better.

    • Tanis Leach says:

      At the most, Mark gives trends based on which ENSO cycle it is (which can be trumped). Granted he was pressured into making a how many days it will snow on one of the podcasts.

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