A Bomb Cyclone, Southern Oregon Snow Storm, & Coldest Thanksgiving Weekend In Years

6pm Sunday…

It’s been a real boring November for weather nerds like me; no storms, little/no mountain snow, mild temps etc…  But it’s been GREAT for anything outside.  I just took a bike ride yesterday with only a light jacket on.

That’s about to change; November is going to go out with some weather action plus cold wintry temps are arriving early this year.  Get your pipes wrapped!  Remember in my previous post I figured that “something was up”?  Sure enough, it appears we’re going to see the coldest Thanksgiving Weekend in at least a decade or two.  And snow may fall to sea level before we finish out the day Tuesday in at least part of the state.

If you’re just looking for a summary, skip to the bottom…

First, there isn’t much of anything interesting happening through Monday, just a little cooler with showers/sun mix all day tomorrow.  I expect 3-5″ snow in Cascades as the sticking snow level drops to around 2,000′.  This is the leading edge of colder air tomorrow.  Take a look at the change in the atmosphere overhead from right now to Thanksgiving

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The real action is Tuesday.  In a span of just 12 hours, a weak area of low pressure well offshore deepens 42 millibars! (Based on ECMWF)  That’s a stunning rate of deepening.  Anything over 24 millibars in 24 hours is considered a “meteorological bomb cyclone”.  No, it’s not a made-up media phrase.  Meteorologists have been watching these storms develop in the north Pacific/Atlantic for decades and that’s the term we’ve always used.  Somehow national media stumbled upon the term a few winters back and decided it was appropriate for the public to hear.  Generally (for good reason) I have kept the word “bomb” out of my on-air forecasts, but apparently it’s okay now.  Here’s what the Euro model looks like Tuesday, click for a more clear view


And the wind forecast showing calculated gusts 80-110 mph mainly offshore near that low pressure center!

Wind Forecast ECMWF HourlyStrong


Green/blue on that previous graphic represents rain/snow. Notice the storm is far enough south that NW Oregon sees only light showers Tuesday.  With such a rapidly deepening storm, it’s possible to get intense precipitation just north of the low center.  That means snow could fall to sea level just north of landfall.  Yep, it’s quite possible Florence or Yachats gets a brief wet snowfall Tuesday and Portland stays dry.  More likely snow will fall along parts of I-5 south of Eugene Tuesday afternoon/night.  Headed to California for Thanksgiving?  Traveling through the Siskiyous Tuesday night could be very rough.

That storm will move through Southern Oregon and into SE Oregon by Wednesday morning.  Depending on the exact track, this could be a big snow storm for parts of central & eastern Oregon.  The ECMWF snow forecast

ECMWF Snow Accumulation

WRF-GFS model is similar


In the Portland metro area we will see a strong easterly wind develop Tuesday evening as that storm approaches.  I doubt it’ll be a damaging wind, but should make for a chilly and windy evening.  It’ll also dry us out nicely too, which leads me to…


The cold air settles in Wednesday through Saturday.  I don’t expect a crazy strong east wind Wednesday/Thursday in the Gorge and east metro, but as high pressure settles east of the Cascades Friday-Sunday it’ll turn into the strongest/coldest of the season so far.  Expect some ice on Gorge waterfalls by Friday.   The long period of cold easterly flow and dry atmosphere shows up nicely on the WRF-GFS cross-section.  That’s Wednesday PM through Sunday PM.


How chilly?  High temperatures will struggle to get above 40 degrees in the metro area, and 30-35 will be more common in the Gorge.  West of the Cascades, overnight lows in calm areas should end up in the 15-25 degree range.  Brrr!


  1. Winter (cold for all + snow for some) is arriving early this year.  An extended period of cold weather arrives Wednesday.
  2. Avoid traveling through SW Oregon (south of Eugene/Roseburg) Tuesday
  3. Avoid traveling south of Ashland on I-5 Tuesday and at least the first half of Wednesday
  4. Expect snowy roads at times anywhere in Eastern Oregon from Tuesday evening through Wednesday
  5. Cascade passes and ski resorts should pick up 10-20″ snow Monday-Wednesday
  6. Sticking snow is unlikely in the metro area below 1,000′ this week

I’m working through the Thanksgiving Weekend so I’ll be keeping a close eye on the weather for you!

Chief Meteorologist Mark Nelsen



59 Responses to A Bomb Cyclone, Southern Oregon Snow Storm, & Coldest Thanksgiving Weekend In Years

  1. Mr Realist says:

    Here we go again with la la land🤣🤣🤣🤣

    Take precautions because we have a earth ending storm coming on the 11th🤯🤯🤯

    Or maybe it wont happen at all?????

  2. W7ENK says:

    Okay, so…

    11 December.

    942mb central pressure.

    This would truly be an historic wallop,
    if it were to come to pass.

    • Snow-Zone Dallas/400ft Roman says:

      WTF looks like a hurricane 👊

    • Jake in Gresham says:

      Stinken’ GFS, always giving us a roller coaster to ride much less a train. Hogwash!

      That would in case us in a blizzard not seen in half a century or maybe more. Idk honestly here

      I call b.s. man :p

      • Andrew in Sandy says:

        But that’s waaaay out… could be gone with the next run. Would be nice to get a good storm or 2 this winter, but no point in getting excited until within a week. and even then things can still fall apart.

    • ♫ La la-la-la-la-la-la la-la land! ♫

  3. W7ENK says:


    Enumclaw, WA this afternoon, as reported by their local newspaper, The Courier-Herald.

  4. Tanis Leach says:

    I have a question:

    A fellow OSU meteorology student informed me that the pressure gradient between North Bend and Gold beach (locations may be wrong, it was in class so I wasn’t paying 100% attention) could be 20 mb gradient vs 13 in the Columbus Day Storm. Said storm had 145 mph gusts (121 mph when converted to 3 second gusts). What could 20 mb do? Yes this is from a reliable scientific source as I saw it but did not jot it down to post here.

    • runrain says:

      I’m guessing the reason these winds won’t be that strong is that the Columbus Day Storm swept north up the coast. This storm is moving west to east. Experts: back me up here?

      • Larry says:

        Don’t worry rain I gotchu 😉

      • Jake in Gresham says:

        That’s correct. It deepened far more and stayed offshore where its South winds scoured Oregon being the most expensive natural disaster (and deadliest) for the State of Oregon costing 1.9 billion in today’s money.

  5. Mr Realist says:

    This could be the story of winter, I don’t think anyone would be surprised.

  6. Tanis Leach says:

    Winter Weather Advisory just issued in the south valley.

  7. WEATHERDAN says:

    NWS has SLE on Northern edge of snow and forecasts up to 1 inch of snow with more further South. Last Thanksgiving like this that I can remember was 1985. Maybe Rod Hill should ask for a raise. Looks like he got the snow part right. The rain part not so much. Peace.

    • boydo3 says:

      That’s my neighborhood! It’s looking worse as you head south toward Crescent City and Acata. If you go to weather underground Port Orford area and check out the Hamlet weather station (number 48), that’s my next door neighbor’s station. We are somewhat sheltered from the strong S. winds but still exposed since we’re just back from the beach and Garrison Lake.

  8. Andrew says:

    Normally I’d be holding out more hope but models tend to be coming into general agreement on southern storm track and I’ve been amazed how accurate things have become. Still will be looking closely at next runs, but feels like forecasters have this one pretty well pegged for now.

  9. Anonymous says:

    ECMWF is now calling for an overrunning snow event for Roland and I in about a weeks’ time.

  10. Andy says:

    I noticed KGW 8 mentioned 1 to 2 inches of snow for areas Salem south on noon news for Tuesday night Wednesday morning. I live in Albany and was thinking Eugene had a better chance of accumulating snow. I will see what the NWS and Mark has to say on the possibilities.

  11. Pat in North Plains says:

    Thanks for the post, Mark. It should be an interesting weekend weather-wise. It’s been awhile.

  12. Larry says:

    I just realized something guys. couldn’t the ground freeze when it gets cold because its wet?

    I mean, think about it. rain should stick around until Tuesday morning or afternoon, and its gonna be CHILLY on Thanksgiving.
    there is a solid day and half worth between rain and below freezing temps (if wed night doesnt hit that mark).

    what does everyone think about this?

    • W7ENK says:

      I think that “solid day and a half worth between rain and below freezing temps” means everything will have a solid day and a half to dry out. Closest you’ll get to frozen streets is a solid skin of ice on any leftover puddles, and that’s about it.

    • Andrew says:

      Yeah. Water typically evaporates a lot faster than it freezes. It takes a unique set of circumstances to create those kind of problems, typically a slushy mess followed by rapid cooling which creates legitimate “layers” of ice on ground. Otherwise, ice is usually confined mainly to puddles. at least that’s always been my observation.

      • Larry says:

        Going back to january 2017 about that snowstorm. the ground at my house was wet, ice started to form, then snow started to fall.
        its a great example describing the type of scenario you were talking about, Andrew.

        Still think frozen streets are a possibility. I just dont see the ground drying out that quickly. hopefully theres no puddles on your roadways!

        Not sure how the POSSIBLE and CHANCE for snow tuesday night would affect a scenario like this, but lets keep it out of the discussion for now.

  13. Roland Derksen says:

    Foggy here this morning and feeling chilly, but the real cold air will be arriving at mid-week. Out here near the coast we probably will see overnight minimums somewhere in the low 20’s or so.

  14. Anonymous says:

    Mark you are the “BOMB”

  15. rmlounsbury says:

    I noticed the NWS Portland Twitter account officially added snow to the valley floor for tomorrow night. So, the NWS curse is active and not in a good way.

  16. Diana F. says:

    All I have to say is FINALLY, and THANK YOU!

  17. W7ENK says:

    WRF-GFS is currently running, and there looks to be quite a bit of cold air dumping into our region from out over the Pacific. That’s generally how we end up with surprise little lows that spin up off the Southern tip of Vancouver Island and meander their way down the Washington and Oregon coastline, sucking up marine moisture and tossing it inland… in other words, SOWT.

    Might be something to watch for in the coming days, since models generally don’t even see it until it’s about to happen.

    • Larry says:

      Is that true? ive never heard of that before. that would be really cool to see a scenario play out like the one you mentioned.

      • W7ENK says:

        That’s what played out repeatedly in December 2008. SOWT (Short Over Water Trajectory) is the one of the most common ways we get snowfall in the Willamette Valley.

    • Andrew in Sandy says:

      Thanks for sharing, I didn’t know this was a thing.

  18. Jason Hougak says:

    Blogs come to a screeching halt… snow showing up on the ground on numerous road cams in Central/ Eastern Oregon.

  19. JohnD says:

    All eyes on the Bomb. Just a little shift north could be a huge game changer! Kelley Bayern (one of the Weagher Conference presenters this year) was alluding to that on her tv segment this morning too.

  20. Andrew says:

    probably doesn’t mean much, but low has moved a little north in each of last four Euro model runs. For something that’s still 48 hours away, that trend seems at least worth keeping an eye on.

  21. Mr Realist says:

    To bad for Portland, I guess he’d to Methford if you want white.

  22. W7ENK says:

    “Bomb cyclone…”

    So much drama!!

    • Jake in Gresham says:

      Hey I’m super excited. Something cool (pun not intended) is happening in the PNW. I felt like I was going to have to move to Alaska (tried actually – no company would take my wretched self).

  23. JERAT416 says:

    Could you imagine what would happen if it hit us directly….would we be talking Columbus day storm, or just a big storm like we see every 20 years or so?

    • Jake in Gresham says:

      If I’m not mistaken that’s what Rob was eluding too regarding the 2008 storm? I’m not sure what track it took (I was in high school and don’t recall).

      I think it was more East to West (which would greatly turn up the gorge). Either way, this is one heck of a storm. About a foot in Bend/Sisters? My thought is I-5 will be shutdown South of Medford.

      • JERAT416 says:

        Could be , December 2008 dumped at least a foot over the course of a week. Well advertised arctic air the models showed a week out, then lots of moisture. That was sure something! Not a lot of wind for the metro area though.

        • Jake in Gresham says:

          I just recall the first storm well of that 2 week event (took forever to thaw here). Here on the East side of town the gorge was something (snow blowing off houses combining with the falling snow into one big haze of white).

          I sometimes couldn’t see across the street to my neighbor’s homes. My sedan went under a drift of 4ft lol.

  24. Jason Hougak says:

    Mark you need to be on the ground reporting when it makes landfall.

  25. Jason Hougak says:

    If the forecast is on track that’s the same area hammered by the intense snowfall last February when Eugene got hit. Areas south in Douglas County piled on the heavy wet snow.

  26. Evan -- Cedar Mill says:

    Even if that low moves a bit north I don’t think we have enough cold air in eastern Oregon. We haven’t had time to build up a reservoir this year.

  27. Tanis Leach says:

    GFS delayed the ice storm till Tuesday of next week, with it switching to snow. I like that better.
    Possible first

  28. Ken in Wood Village says:

    Hopefully the trend to the North continues and the Portland area and we see some snow flying 🙂

  29. K says:

    Cross-cascade gradients look very intense. Could this bring us some pretty windy conditions on Tuesday? I wonder…

    • paulbeugene says:

      Keeping an eye on things as they unfold in next 72 hours. Seems we will be on the northern fringe of precipitation here in Eugene. Wouldn’t be a surprise if we have at least a skiff of snow on ground in south Willamette valley on thanksgiving morning.

      This could be a preview of things to come in about 2-3 weeks. Long range models seem to suggest building 500mb heights up toward Anchorage. There should be an ample supply of cold air building over the interior of western Canada

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