One “Bomb Cyclone” Down, One to Go!

October 21, 2021

10pm Thursday…

After a very warm day with some lower 70s in the metro area, moderate to heavy rain has arrived with a Pacific weather system. I expect steady rain for a few more hours, then the usual scattered showers behind the front the rest of tonight. Expect more showers Friday but decreasing as the day goes on.


  1. You may hear/see something about a powerful storm (or worst ever?) for the Pacific Northwest this weekend. No, there is not a mega-storm on the way for the region. THERE WILL BE A HUGE STORM OFFSHORE, but it’s far enough away that we get typical wind/rain. No big storm.
  2. Things are moving fast/furious now with a strong Pacific jet stream overhead, so weather will be changing quickly from day to day…make sure you are paying attention to forecasts.

Tonight’s front is the leftovers of a powerful “Bomb Cyclone” that moved through the northeast Pacific ocean well west of the Pacific Northwest. A bomb cyclone is simply an area of low pressure that deepens “explosively” in a short period of time. Anything over a 24 millibar drop 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 and I sure used it last night! So that first cyclone is now weakening after bottoming out at around 950 millibars well west of the 130W “danger zone”. When deep low pressure centers track through this area we watch very closely!

Our big windstorms west of the Cascades almost always occur when a low pressure center tracks within this area

Now this is amazing; we have a second (and stronger!) bomb cyclone developing Saturday night and Sunday. Yep, that’s two huge storms relatively close to the region in less than 4 days. Highly unusual.

The latest global model forecasts are in remarkable agreement this evening. All are forecasting a surface low pressure center to drop from around 993 millibars Saturday morning to 943, yes 943, millibars. You can see the track of both lows, notice this 2nd one will be a bit closer

That 943 millibar value will probably be an all-time record deep low pressure so close to the region. For comparison, the Columbus Day Storm was “only” around 960 mb, but less than 50 miles off the coastline! Tracks of the last three major regional windstorms…all well inside 130W.

Ryan Maue, a meteorologist with, checked lowest surface pressure in the 1950-2021 record. He tweeted “the minimum central pressure of 944 millibars from next storm off Pacific Northwest coast will likely be the deepest/most intense in this area of ocean at 45°N and 135°W at least since 1950” The graphic he tweeted shows that boxed area. Plus you see the lowest pressure right up against our coastline (the past 70 years) was that 960mb during the Columbus Day Storm.

This is all interesting stuff of course, but what’s the effect along the coastline and interior? A gusty east wind Sunday morning turns breezy from the south Sunday afternoon and Monday. Yet the strong wind field remains offshore through the event.

The ECMWF model shows this well, gusts over 100 mph over the open ocean, but under 70 mph along the Oregon coastline. This shows accumulated gusts (highest gust) from now through 5pm Sunday.

Most likely we’ll see gusts 55-65 mph along the beaches and 30-40 in the valleys. That’s relatively weak of course, not a windstorm, but enough to make for a windy Sunday afternoon!

That’s it for now, I’ll be off tomorrow but back at work Saturday and Sunday tracking our very wet weather pattern.

Chief Meteorologist Mark Nelsen