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

November 24, 2019

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