Intense, But Small Low Pressure System and Strong Front Brings Extensive Power Outages around Western WA

It's just after midnight winds are really blowing out there now.....I can hear branches snapping.  Lights are flashing on the horizon and it's not lightning....it is the green colors of transformer fuses blowing.

By 1 AM about 67,000 Seattle City Light Customers have lost power and roughly 308000 Puget Sound Energy customers were in the dark.'  A major power outage for the region.




Winds are gusting to 50-60 mph last night.  The max winds through 5 AM are shown below.  Lots in the 40-50 mph, some as high as the mid-60s.


But if you want to be impressed, the max wind gust hit 121 mph at Alpental Summit (see below).   That is serious wind.


The peak winds at Seattle's West Point reached 51 knot (59 mph)...and peak wind on the Evergreen Floating bridge got to 56 mph.



Where did the strong winds come from?   A small, but intense, low pressure system passed just to our north, producing a large north-south pressure difference (gradient) over western Washington (see forecast map of sea level pressure at 10 PM))


Let me be honest.....meteorological guidance underplayed this seriously.  We knew it would be windy, but the forecast models (such as the UW ensemble) were only suggesting sustained winds of 15-20 knots with gusts to 25-35 kt (see UW ensemble forecast from yesterday morning).  Time is on the x-axis and 06/13 was 10 PM last night.  This shows the forecast of sustained winds (averaged over minutes) at Seattle Tacoma Airport, where the max sustained wind got to 28 knots.


Yesterday evening, National Weather Service forecasters in Seattle could see from the satellite imagery that the low was more intense and tracking upon an optimal path and put out a wind advisory.  

Below is the water vapor image at 10:30 PM last night.  It shows the amount of water vapor in the middle to upper troposphere (roughly 15,000 to 30,000 ft).  There was a pronounced and well defined "dry slot", which shows strong descending air behind the storm....a sign of strength.  The low center is generally at the apex of the dry slot.  This was threatening for western Washington and a short-term warning of the blow that would follow.


Importantly, the European model (ECMWF) produced a far better forecast than the American GFS.  Here are are the maximum winds during the event from the European model initialized (started) at 4 AM Tuesday. Gusts reaching to the mid 50s (mph) over Puget Sound and much higher over the mountains.   Good forecast.

Far less in the U.S. model, with winds only gusting to around 40 mph over Puget Sound.  The European Model did far better with the intensity and track of the low.   I often talk about how the U.S. needs to improve its forecasting capability in this blog...this is a good example to keep in mind.




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