November 25, 2019

A Bomb Cyclone Will Hit the Southern Oregon Coast

An explosively developing bomb-cyclone will hit the southern Oregon coast tomorrow, with hurricane-force wind gusts, towering waves, and lots of precipitation.

The term "meteorological bomb" is given to a midlatitude cyclone whose central pressure declines by more than 24 millibars (or 24 hPa) in 24 hours (there is a latitude dependence of the criterion, but this is close enough).  This storm is going to blow that criterion away.

Virtually all the models agree on this extraordinary strengthening, so confidence it quite high.  And there are some aspects of this storm that are very unusual. Let me show you the details.

The initial step in the development of the storm, a process called cyclogenesis, is occurring as I write this blog. The latest forecast for 4 PM today (below) shows an extremely weak initial development on a preexisting warm front, with the low pressure center being a very modest 1022 hPa (I put a blue oval around the developing storm in the weather map below, which shows pressure (solid lines), temperature (shading) and surface winds).

Fast forwarding to 3 AM, the low center pressure had deepened to 1009 hPa (13 hPa in 11 hours).

But now the storm is ready to explode.  By 10 AM Tuesday, the storm's central pressure had plummeted to 983 hPa (39 hPa in 18 hour!).   Well exceeding the requirements to become a bomb cyclone.

And as the storm makes landfall around 6 PM Tuesday, the storm is predicted to be around 980 hPa.  In fact, I am only showing you the medium resolution simulation (12-km grid spacing).  The higher resolution domains drop the pressure to around 978 hPa at landfall.   

Notice the HUGE pressure gradients (pressure differences) associated with the storm.  These will produce tremendous winds in the coastal zone and immediately offshore.  You see the blue colors?  That is cold air that will be streaming from the northwest at the same time, sucked to the southwest by the low pressure center.  In fact, the high pressure associated with the cold air is contributing to the strong pressure gradients and strong winds.

Talking about the winds, here is the wind gust forecast for 5 PM tomorrow (Tuesday).  Gusts to 70 knots (81 mph) to the west/southwest low center.  In the field, this is known as the "poisonous tale of the bent-back occlusion."   Repeat that to your friends...they will be impressed.

The strong winds will rev up substantial wave activity, reaching 11 meters (36 feet) along the coast.  Particularly impressive, considering short-duration of the winds from this fast moving storm.

And there is more, much more.  The storm will bring substantial precipitation from southern Oregon into northern California (see below), reaching 2-5 inches in the Sierra Nevada.  Not much in Washington.

And with cold air streaming in from the northeast, large amounts of snow will fall in the Oregon Cascades, the Siskiyou Mountains, and the Sierra Nevada.  In some places, several feet (see forecast of the total snowfall through noon Wednesday).  If you are planning on driving south from Oregon into California or across the Sierra Nevada, bring your chains.

The National Weather Service forecast summary for the region has almost every  type of warning imaginable, from high wind warnings, storm warnings, and winter weather warnings, to high surface warnings and more.

An unusual aspect of this storm is its track--from the west/northwest.  Most major cyclones this time of the years comes from the southwest.

Anyway, a major event--but what should we call it?  A day later, it could be the Thanksgiving Eve storm.  Will have to think about it....


  1. Impressive storm. November is the time for them.

    Perhaps the "poisonous tale of the bent-back occlusion" should be the "poisonous tail of the bent-back occlusion" or maybe it is a tale.

  2. I thought the term was "...back-bent occlusion?"

    I think we should call it the Thanksgiving Eve-Eve Storm.

  3. The ECMWF forecast from 6 days ago nailed this storm (more or less). It's interesting when the long range deterministic model will pick the right ensemble member, but intermediate runs miss it.

  4. All the warnings are issued, but where is the heat advisory and red flag warnings? Or the hurricane warning?

  5. let's see..."Duck, Duck-Goosed"? Or,"Fowl Weather Wednesday"?
    I could go on ad nauseum..

  6. hey Dr Mass,

    Is the upcoming cold front as severe as what happened via the Fraser gap about a year or two ago?

    cheers, Bert

  7. Interesting storm considering the 'blob' lurking off the coast. Reminds me of the Ore-Cal Bomb Cyclone of 1999. 50ft NNW swell down the entire west coast, and at a bizarre angle for such a massive swell.

  8. The sit at home next to the fire have a beer and and look out the window storm.

  9. Bomb Cyclone- New term, invented by the media?

    1. No, it is not invented by the media, although the terminology certainly catches everyone's attention.

  10. Hmmmm... no electricity, too windy for deep frying outside, ... maybe no turkey for some folks. Hope everyone stays safe.

  11. hey cliff what typ of winds would we haft to have for this to push up toward washingtion state and how much snow would drop question i need awnserd

  12. The I-Hope-This-Damn-Bird-Thaws-In-Time storm.

  13. There is always weather, just not always in here.

  14. I've been on the Oregon Coast when storms like this one have hit. Spectacular, dangerous, intense and thrilling. There is something both terrifying and magical about facing into the winds of a major storm. Good luck to everyone who ends up within the track of this beast.

  15. Cliff, how similar is this to the Columbus day storm of 1962? Is there any possibility of it tracking north along the coast

  16. I see a fan of Mark Nelsens' weather blog in Oregon doesn't mind checking out Cliffs' blog in Washington.

  17. How about: "The Turkey Tom Bomb Storm"

  18. Cliff, I like the Thanksgiving Double Eve Bomb. Hope everyone stays safe.

  19. We shall see. I am in the Rogue Valley. I am leaning more towards. Must to do about nothing...

  20. Minimum temp at my location in NW Bellingham was 31.8F. Temp was freezing from around 445 until 550.

  21. The current NWS discussion is forecast maximum lowest pressure of 972mb (or 28.7" of mercury!!!), which would be an all time low pressure for this area.

    Keep an eye on Cape Blanco on the southern Oregon coast. It receives 100 mph winds on a somewhat regular basis, so it will likely really get blasted on this one. Dr. Mass has many references to Blanco in this discussion of windstorms:


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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