September 25, 2013

Unusual Early Season Heavy Rainfall Event Heading for the Pacific Northwest

It is quite unusual to get major rainfall events in our region during September, but a very wet pattern looks probable over the region this weekend and early next week.  Over a 72h period, some locations in the Olympics and north Cascades could getting a half foot or more of rain and minor flooding is possible in vulnerable locations.  The National Weather Service put a hydrological notice today for the upcoming period...a good call.

Thursday will be a nice day with sunny skies and highs in the mid 60s.   Get out and enjoy it.  It will be the last one for a while.  Starting Friday morning, a series of moderate to heavy rainy periods will occur over our region.

Let's examine the latest UW WRF numerical model forecasts.   Here is the 24h precipitation ending Saturday morning at 5 AM.   1-2 inches in the mountains, with a some limited locations getting a bit more.  Oregon will remain essentially dry during the period. 

 During the next 24h, ending 5 AM Sunday, the rain does not quit, it intensifies,
with some locations in the Olympics and north Cascades getting 5-10 inches.   Very wet in southwest British Columbia as well.

The rain over the next day (ending 5 AM Monday) heads it is Oregon's turn to get inundated.  And yes, it is still raining to the north.

Ready to be impressed?  Here is the 72h total precipitation ending Monday morning at 5 AM.  Wow...large section of the Olympics, coastal mountains, and north Cascades (and the Coast Mountains of BC) end up with 5-10 inches.  This is a lot anytime of the year and quite remarkable for September.  Some daily records will probably be set.

These precipitation amounts will be sufficient to drive some local rivers to near bankful.  The National Weather Service is already warning that a number of rivers will get to "action levels"-- high enough for some mitigation by local agencies.  To illustrate, here is the current and predicted flow levels for the Snoqualmie River near Carnation.  Anyway, keep tuned as the forecasts are updated...and don't plan a hike over the weekend in western Washington!

Bellingham Talk on October 15th

     I will be giving a public talk on "The Future of Weather Forecasting" in Bellingham on October 15th.    In this talk, I will discuss the development of weather prediction from folk sayings to numerical weather prediction, and describe what I think will happen over the next decades.  For more information, go here.


  1. Very unusual for being this cool and rain amounts
    this early in fall. Have lived here for over 50 yes now.

  2. Cliff,
    Are you going to post a video of your talk online?
    Would love to be able to view it.

  3. Oh, my. I'm so not ready for this. Still hoped to get in one last hike, one last seakayaking excursion, one last *something* that works with our generally-pleasant weather at this time of year. And so much for our long-delayed exterior house paint project!

    Any glimmer of hope in the long-range forecast, Cliff? Pretty please? ;-)

  4. Thankee, Cliff! Sump pumps are raring to go. Hoping to see enough water to test newfangled pump-initiated siphon, though I suppose I should be careful what I wish for...

  5. Cliff, I notice very unusual, radial features on the NEXRAD radar starting at 8:30 PM Thursday night. I've never seen these before. What is happening?


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