Tuesday, November 17, 2015
|Credit: Seattle National Weather Service Forecast Office|
Things are really ramping up now throughout Western Washington. The all-important PDX-BLI gradient, which was forecast to max out at 14-18 hPa, is already at 18 hPa, and continues to slowly rise. There is a chance that the gradient could reach 19 hPa at some point today. Regardless of what it reaches, today will be the windiest day of the year so far for many people in Western Washington.
However, I want to make one thing clear: this windstorm will not be on par with the Columbus Day, Inauguration Day, or Hanukkah Eve storms, which are generally regarded as the three most intense storms to hit the Puget Sound region in the last 60 years. It will be stronger in most places than the August 29th windstorm that knocked out power to 500,000 people, but because the deciduous trees have lost many of their leaves, it will not be nearly as destructive. On the other hand, soils are saturated from the recent heavy rain, particularly soils in the Cascades and Olympics, making trees more prone to toppling under high winds. Either way, at least 100,000 people will lose power, but definitely not 1,000,000.
First, let’s talk about rain. Moderate rain is falling over the lowlands, and the heavy rain is falling in the mountains. Just like the event this past weekend, there is relatively little rain over the Pacific, but once that moist air encounters some terrain, rain starts pouring down. You can also see a thin line of precipitation off the coast, which marks the location of a very strong cold front. More on that later.
Here are some 24-hour totals from around the region. The area between central Whidbey Island and Seattle has been relatively shadowed from the rainfall over the past 24 hours, but as the radar image shows, Seattle is now mostly out of the rain shadow, which is mainly situated over Everett. The mountains, coast, and lowlands from Seattle south are getting the heaviest rain right now, with one gauge near Lake Quinalt on the Olympics picking up 6.40 inches! This is the same gauge that received 12 inches in 24 hours this past weekend, so it’s no coincidence that it has received the heaviest rainfall thus far.
Due to all this rain, saturated soils, and the rivers already running high from last weekend, we currently have 8 flood warnings across the area. I’ve listed them below.
Skokomish River near Potlatch affecting Mason County
Snoqualmie River near Carnation affecting King County
Snoqualmie River near the Falls affecting King County
Skykomish River near Gold Bar affecting Snohomish County
Stillaguamish River at Arlington affecting Snohomish County
Chehalis River at Porter affecting Grays Harbor County
Elwha River at McDonald Bridge affecting Clallam County
Grays River near Rosburg affecting Wahkiakum County
Now that we’ve got that covered, let’s talk about the main story for today: wind.
It’s now 11:26 at my house, and winds are really starting to pick up.
As you can see, winds are pretty gusty around Washington… we recently had a 55 mph gust at West Point in Magnolia… but nothing out of the ordinary. Most peak gusts in the lowlands thus far have been 30-50 mph. Sea-Tac has hit 40, and Everett (Paine Field) has hit 53.
I expect winds to really start ramping up by noon as the cold front associated with this storm draws closer. There will be higher pressure gradients and the atmosphere will be less stable, allowing for some of those gusty winds aloft to make it down to the surface.
520 Bridge is still open, but I think they will close soon… they are getting sustained winds of 39 mph with gusts to 47 as of 11:40. They need 15 minutes of frequent 50+ mph gusts to close.
|Credit: Seattle City Light|
|Credit: Seattle City Light|
|Valid 01:00 pm PST, Tue 17 Nov 2015 – 9hr Fcst
Credit: UW Atmospheric Sciences