October 16, 2009

A very wet Saturday (and the Green River will not flood)

The latest high resolution forecast model runs are in. As are the new ensemble predictions (running many lower-resolution versions to determine the uncertainty of the forecasts). The bottom line...it will be quite wet during the next 24-36h...including the central Puget Sound region, the Olympics, and the Cascades.

Lets start with the latest satellite picture (attached)--you can see the plume of moisture that is approaching us. You can also see a wave in the clouds--that is a developing weather disturbance that will move through tomorrow and enhance the rain.

I will show you a graphic now I have never shown before...from the new RAINWATCH system my group is developing for Seattle Public Utilities (who are very concerned and proactive about heavy precipitation and flooding in the City). This shows you the rainfall over the past twelve hours based on combining the local radar and surface rain gauges. You can see the rain shadow NE of the Olympics and the heavier rain over Seattle and the central Cascades (keep in mind the blockage of the radar SE of the Olympics and over portions of the Cascades). Many locations have gotten over .5 inches in the later regions, some with well over an inch. But there will be a lot more.
Next the latest information from the high resolution forecasts. The precipitation may back off a bit tonight and then hit hard tomorrow as the disturbances comes in. The 24h totals ending tomorrow at 5 PM (Saturday) show a drenching...with 1.26-.2.5 inches (pink) over many locations (like central Puget Sound), with some places getting 2.5-5 inches. The subsequent 24 hours (ending 5 PM Sunday) brings precipitation, but far less (graphic). A frontal passage late on Saturday will transition us to a drier regime on Sunday with scattered showers. So that is the day to get out (and dry out). Maybe a hike in the Olympics.

So lets talk about the Green River...there should NOT be flooding from this. The river is very low now and this event is not the equal of the big ones. There is plenty of room behind the dam to store water right now.

Around the urban core there could be some localized street flooding...particularly if leaves clog the drains...so it is a very good idea to clean the drains in front of where you live or work.


  1. Thanks for the update, I look forward to a nice fall drenching! Looks like the visit to the pumpkin patch will have to happen on Sunday!

  2. All you need to say is: It's going to be wet. Nuff said. The charts look cool, but are pretty much meaningless to most of us. Thanks anyway.

  3. The charts are great! They appeal to my inner Nerd. Yesterdays 4km WRF predicted a big blast of southeast surface wind just north of Port Townsend. When I passed there today, I observed a howling jet of surface wind in the exact place where the WRF said it would be. My sincere compliments to the entire UW development team, that's worked so hard on the WRF model.

  4. cprimm almost reminds me of another user that no longer posts on this blog... Please continue to post as much information as your time allows, I enjoying seeing the charts and other information that I can't get from the local news websites.


  5. If it weren`t for weather charts/ graphics, then it would be hard to forecast or even give mention of where it will or wont rain or where a certain storm will end up. Bottom line here is that these are very useful and wonderful to have. They serve greatly in the world of weather! :o)

  6. Cliff, I really love the graphs you choose to show us. As I've followed your blog for the past 18? months, I've learned how to read those charts and can recognize quickly a "big deal" from same-o, same-o. That knowledge really enhances what I've gotten from your book, and the neighborhood kids LOVE to ask me about the weather now. :-) They are learning too!! I try to sneak some math in on them.....

  7. I've got to say, though, what the heck is wrong with Probcast? I'll grant you that it shows both the highest probability of precipitation that I have seen AND the highest amounts... but when your chart calls for 2.5" in my area in 24 hours, and Probcast says the likely amount is 0.35" with the possibility of as much as 2.07", something is out of whack.

    My rain gauge is not very good, so I will be watching the much better Phantom Lake Elementary School gauge this weekend. It's 0.8 miles away and it will give me a good way to benchmark Probcast.

    Cliff, I'd love to hear what causes those big variances in the Probcast forecast (I'm in ZIP 98008 just west of the middle of Lake Sammamish). Thanks!

  8. Cliff

    is RAINWATCH a public available "product" or still research only with limited distribution?

    I see net searches (for what is a common term) even when limited to particular domains (inclding your name!). don't even show any papers or presentations on RAINWATCH.

    Any links would be appreciated.

  9. i can tell that this system is tropical, its feels so 'soupy' and the downpours woke us up this morning. but after a dry summer, we need it but the warmth can go away, i want it be in the 40's and stormy.

  10. Passed up the High Resolution here in Bellingham:)


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

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