October 28, 2010

Major Rain and Flooding Event Approaching

Well, I was having some fun in my last blog, but this one will be serious. The reason? A major rain and potential flooding event may be coming, one that could impact some people's lives. But some uncertainty remains, and I will try to be upfront with that as well.

During the next few days a disturbance off of Asia (Typhoon Chaba) will move northward, turn into a midlatitude cyclone and amplify into an extraordinarily deep low pressure center (see graphic). We are talking about 939 mb! (compare that to the 955 mb over the Midwest that everyone was excited about two days ago). There are so many isobars near that low the graphic is turning black!

The monster storm, huge in scale and possessing hurricane force winds, will produce giant waves--greater than 50 ft high. I could fill an entire blog about this storm...but there is a more acute worry here at home.

As the low pushes into the Gulf of Alaska it will result in the establishment of a very strong, moist current heading right for our region. You know the names---atmospheric river is the generic term and our version is often called a pineapple express. The next graphic presents the early stages of this feature (Monday AM)....the total amount of water vapor in a vertical column is being shown:

You can see the current of moist air heading right for us.

Here is the 24-h rainfall prediction ending at 5 AM Tuesday. Red indicates 5-10 inches of precipitation over the Olympics, north Cascades, and mountains of southern BC. Precip decreases rapidly to the south.

A looks at a closer view for the same period below. A profound rainshadow will also exist NE of the Olympics. I am sure the National Weather Service will be putting out some statements on potential flooding of rivers coming off the Olympics and N. Cascades. At this point it does not look like a situation that would produce urban flooding over the Puget Sound population areas.

The plume of atmospheric river air over us on Monday and Tuesday will feel warm, moist....almost tropical after the cold weather. Freezing levels will rise to 8-10,0000 ft and a lot of the new snow will melt (sorry snow lovers).

I should be clear that there is often a lot of uncertainty with these cases of tropical storms converting into midlatitude systems. But the computer models have really locked on to this solution and we are close enough now in time that I am believing it. Lets face it, it is really extraordinary we can do this at all.


  1. This is a pattern will see again this coming winter leading to the dreaded "rain on snow" events that affect us in the the greater NW. January and February are the prime months for this to happen. Enjoy December skiing then make reservations for Hawaii. Cheeers!

  2. Any winds expected inland with this event?

  3. You got your wish. The data review shows the latest storm just missed the all-time record:
    Data Review Reveals Midwest Cyclone Missed All-Time Record by 0.01"

  4. The MIMIC TPW product does a good job of showing the atmospheric river.


  5. 50 ft. waves? Does this mean the Washington coast would be a destination for weather watching this weekend? Or is it going to be delayed a bit?

  6. What about wind? It's obvious that there are serious wind issues with the storm itself (I hope the crabbers or fishermen up there, if any are out at this time, are careful), but will we see any significant wind here?

  7. chaba is still near tokyo--how does it arrive on monday

  8. @signalius

    The swell approaching is expected to peak in the low twenties (feet) on Tuesday. A little smaller than last weeks. Last Monday combined seas of 30 foot swells were forecasted. In some areas it is possible the inoming swell could translate into 50 foot breaking waves. Not everywhere though. At this point, tuesday would be the day for storm watching. The coast will be quite the site to see. Especially if you could make it down to Lincoln City oregon to watch the Nelscott big wave surfing competition. This will be the first year the competition is paddle only, meaning, no jet skis will be used to tow surfers into the approaching swells. It should be really interesting! :)


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