Some Re-freezing On Roads Overnight

3:15pm Update…

The Highlights:

  • Many streets are wet in the metro area, especially where we’ve seen drizzle (west side right now)
  • Temperatures are hovering right around freezing at the lowest elevations
  • Temperatures are slightly below freezing on the hills
  • Those hilly areas may see roads freeze up soon after sunset 5-7pm.  Watch out if you are driving after dark off main roads and at any elevation!
  • Even some lower spots may see roads freeze after dark.   Be careful the next few hours!
  • Little or no new freezing drizzle or flurries are expected through tonight
  • Tomorrow morning’s commute is a big question mark, it’s possible there are lots of icy spots if all areas drop below 32 degrees again.  Give yourself a little extra time tomorrow morning

It’s been an interesting 8 hours, lots of flurries, although the precipitation has barely been measurable.  Now some spots have turned over to drizzle.  So plenty of wet streets and roads.  Yet just about the entire metro area is at or slightly below freezing. 


So how does it drizzle at 31 or 32 degrees and not freeze on roads and other surfaces?  It’s a dirty little meteorological secret that during the daytime it needs to be around 30 degrees (or even a little lower) for liquid rain/drizzle to freeze to a surface.  I learned this during an ice storm in January 2005 when reporters kept saying the street and sidewalk was melting slightly and it was 29 degrees.  It gets  just barely warm enough during the daylight hours that the weak sun that makes it through the clouds is enough to keep surfaces warmer than freezing.   Here’s a good example using and ODOT road sensor:

This is I-205 and Division street showing the air temperature briefly peaked at 33 this afternoon but the road temp was up to 37.  It’ll drop back to the air temperature after sunset, thus my concern about refreezing in the highlights above.

As for precipitation, we shouldn’t get anything other than what we have already seen.  Flurries or spots of freezing drizzle.

Chief Meteorologist Mark Nelsen

90 Responses to Some Re-freezing On Roads Overnight

  1. Ron says:

    I wish I had Mark Brightwood in my Science classes. Might be learnin’ somethin’ about micro-climates and the scientific method. I approve this message.

  2. ErinK says:

    This might have been answered before but how is it not snowing when its 32 (or less) and its “raining”? I have seen it snow at 35 before.

  3. Jclack says:

    My temp has been remarkably steady for 2 hours… not even a 0.1 degree move… 32.7. Roads fine but ice forming on grass, cars, etc..

  4. W7ENK says:

    Eeek!! Getting super icy on the West side now…

  5. Tyler Mode in Battle Ground says:

    Upper sensor is really on the rise…the inversion is settling down…

  6. Tyler Mode in Battle Ground says:

    A balmy 44 at the 7000′ level on Mt. Hood.

    31 here.

  7. M says:

    Any thoughts on the probability of school delays tomorrow morning due to poor road conditions?

  8. Tyler Mode in Battle Ground says:

    I guess a good reminder is that 32 is the melting point of water, not the freezing point. Water can easily be liquid well below 32, but not usually frozen too far above.

    • IceCold says:

      ” Water can easily be liquid well below 32″


      You need to take a Physics class.

    • David B. says:

      @IceCold: No, Tyler is right. It’s called supercooling.

    • Tyler Mode in Battle Ground says:

      But the property of water that “is most fascinating is that you can cool it down well below 32 degrees Fahrenheit [zero Celsius] and it still remains a liquid,” says Molinero.

    • IceCold says:

      “tiny amounts of liquid water theoretically still might be present even as temperatures plunge below minus 48 C (minus 55 F) and almost all the water has turned solid”

      I think you are missing the point of the article and trying to make it mean something that it is not saying.

    • Rich says:

      Two weekend’s ago I was in Redmond. We left 4 bottles of water in a cooler outside wile it was 9 degrees outside over night. We woke up in the morning and found the bottles all still in liquid form. When we disturbed the idle state, they instantly froze solid. It was pretty cool… still not sure how it happened…

    • W7ENK says:

      Actually, you’re both wrong. Supercooled water, yes. Supercooled liquid water falling from the sky, also yes. BUT, once the balance of the water molecules in those supercooled droplets gets disrupted, either by coming into contact with something or impurities being introduced to the water, it will near-instantly turn to a solid = ice.

      I have placed bottles of water in my freezer over night, pulled them out in the morning and they were still liquid. All you have to do is squeeze the bottle and dent the plastic in one spot, and the water will rapidly turn to a solid ice crystal, radiating from the site of impact. So weird, and SO awesome!

    • IceCold says:

      Yes, that is correct.

    • Rich says:

      Well thank you W7, mystery solved.

    • W7ENK says:

      Hahaha!! 😆 Wow Rich, we must have been on the same wavelength — we posted our water bottle stories at exactly the same time!

  9. W7ENK says:

    A little treat for all of you:

    Use this site to monitor all the Police/Fire/Medical activity tonight, know where all the trouble spots are, etc… Everything pops up on the interactive map, and you can even listen to live radio traffic. If nothing else, it’s fun for an evening shut in by the weather. Enjoy! 🙂

  10. alohabb says:

    Lots if drizzle falling, streets very wet , temps at 32 and have been for a while but no signs of freezing? Wierd

  11. W7ENK says:

    Portland Police are now starting with the road closures due to ice; Skyline is the first, what’s next?

  12. Thomyee says:

    Why is the freezing rain advisory expiring at midnight. Is it supposed to warm up? I guess it will be safe at 12:01 am.

  13. KPTV Tower Temps
    As of 5 PM (1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 28.2 (27.7 at 4:00 PM)
    Middle Sensor(1473′) 27.1 (27.0 at 4:00 PM)
    Lower Sensor(1043′) 28.6 (28.9 at 4:00 PM)
    No real changes still remain well below freezing.

    02z(6 PM) Upper Air Analysis(Observed over PDX)
    925mb: -1.3c
    850mb: -2.2c
    700mb: +3.7c
    500mb: -16.7c

    Looking at the PDX, Langley Hill, and Seattle Radar I sure see a lot more low-level moisture possibly coming tonight than previously thought. Well I seem to think so anyhow.

  14. swift says:

    Looks like PDX only hit a high of 33 today with light snow/flurries all day long. I notice the Mets all have us dry the rest of the week even with fog. It wouldn’t surprise me one bit if we got a repeat of today the next couple of days. It also looks like KGW’s FutureCast called the event and had snow around the region for today but it was the only model calling it. Did any other models other than KGW’s call it? Watch the video.

    • Garden Home 200' says:

      KOINs mets, called it last night on: 6 and 11.. weather cast.
      Cu dos to them. 30.2 last night, 35.1 this afternoon. 33.8 right now.
      Monitoring a few different sources, I recognize how difficult it is to nail a forecast, when we have these types of conditions….
      It sure appears that with freezing temps tonight it is going to be
      a mess in the morning. Safety First 🙂

    • Garden Home 200' says:

      Mark, I think so …. forgive me for not being 100%…sure…

  15. W7ENK says:

    BOOM! There it is…

    Everything not immediately coupled to the ground is beginning to ice over now, 31 degrees. The roads probably aren’t far behind.

  16. Tyler Mode in Battle Ground says:

    Drizzle and light rain now…and 31 degrees. I can see the ice forming on the truck…

  17. kdi says:

    Weirdness: a client of mine in se idaho was -19 last night. Western oregon sees freezing fog. And here on a plateau outside of maupin it was 45 with a 20 mph swesterly. Odd variance in the pnw. And a client outside of lewiston had real snow all day.

  18. SeDrools says:

    Milwaukie Dome in full effect, straight rain/drizzle.

  19. Tyler Mode in Battle Ground says:

    Freezing rain at VUO, freezing drizzle at PDX.

  20. KPTV Tower Temps
    As of 4 PM (1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 27.7 (27.5 at 3:00 PM)
    Middle Sensor(1473′) 27.0 (26.8 at 3:00 PM)
    Lower Sensor(1043′) 28.9 (28.4 at 3:00 PM)
    Gradual warming, but still remain well below freezing.

    01z(5 PM) Upper Air Analysis(Observed over PDX)
    925mb: -1.9c
    850mb: -2.4c
    700mb: +2.7c
    500mb: -17.2c

  21. Did the ecmwf not update at 12z today?

  22. IR Loop
    It sure looks like to me that there might be more moisture and it may swing down from the north this evening/overnight. Hmmm…..

  23. Snowing again…. Radar looks decent. Obviously the cold layer is still deep enough so we’re not seeing sleet or freezing rain with this.

  24. Tyler Mode in Battle Ground says:

    Heaviest snow of the day falling now.

  25. runrain says:

    Getting a silvery layer of sleet/freezing rain on the deck now in Happy Valley.

  26. KPTV Tower Temps
    As of 3 PM (1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 27.5 (26.8 at 2:00 PM)
    Middle Sensor(1473′) 26.8 (26.2 at 2:00 PM)
    Lower Sensor(1043′) 28.4 (27.7 at 2:00 PM)
    Gradual warming, but still remain well below freezing.

    00z(4 PM) Upper Air Analysis(Observed over PDX)
    925mb: -1.9c
    850mb: -2.6c
    700mb: +2.9c
    500mb: -17.2c
    Temps aloft warming. Inversion episode is beginning….

  27. cgavic says:

    Reporting from 1,100 ft sandy
    Ok… was supposed to be clear no worries about low elevation whatever.

    O/nite 18 (night before 16. 25 was that day’s hi) hi 28. Afternoon snow showers and freezing rain.
    Lets hope we get clear cold weather for the balance of the week. Then bring in another snow event.

  28. Tom (NE Portland) says:

    I’m sure glad we saw some decent snow this morning even though it didn’t accumulate. It’s just too bad today has turned into an ugly, soupy mess.

  29. Timmy_Supercell (Klamath Falls @ 4200') says:

    Oh should be very fun this evening. The ones from CA who have never seen ice or snow, have fun driving!

  30. TygrrLilley says:

    I was beyond stoked to wake up to snow falling on the eastside of Vancouver!! I didn’t even care that it wasn’t really sticking. LOL!! And you can call it flurries, freezing drizzle, or whatever you’d like, but I LOVE SNOW!!!!!

  31. pappoose in scappoose says:

    “As for precipitation, we shouldn’t get anything other than what we have already seen.”

    What we’ve already seen is SNOW!!

  32. runrain says:

    Looks like maybe another little batch of something dropping in on us now. And all that gunk in central Washington. Will it disipate much like this mornings did?

  33. Ben T says:

    So this clearly means we will get heavy snow. Bring on 6 inches of snow!

  34. octballcoach says:

    Any mariners out there? This one looks ugly….

  35. W7ENK says:

    Should be fun…

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