Windstorm Update

Sunday, September 29, 2013
10:36 a.m.

What are more delicious? Apples or mangoes?

Mangoes, of course! They are juicier, sweeter, and slipperier than our state fruit. Also, they are imported, and just the thought of eating something that came from Thailand automatically makes it more delicious.
Apples aren’t too bad though. They have anti-doctor properties and permeate the Pacific Northwest. They are cheap and local, and they are therefore under-appreciated. Once you get over the sobering fact that the most awesome fruit grows somewhere between the tropics of Cancer and Capricorn, apples don’t seem too bad.
This is the analogy I came up with for today’s UW model runs. Apples are to mangoes as the WRF-GFS is to the MM5-NAM. Let me show you what I mean.
The 12z WRF-GFS is about on par with what we saw last night… maybe a wee bit weaker. This sort of track would give storm force winds to the coast with lesser gales inland. Of course, gales are nothing to snicker at, but we aren’t talking any record winds here. The gradients are not nearly tight enough over our area. The place that has the best shot of receiving some damaging winds would be Clayoquot Sound and Tofino.
Valid 08:00 pm PDT, Sun 29 Sep 2013 – 15hr Fcst: 1000-500mb thickness, SLP (hPa). UW WRF-GFS 12km Resolution: Initialized 12z Sun 29 Sep 2013. Retrieved from the (University of Washington) Pacific Northwest Environmental Forecasts and Observations website. Chart URL: http://www.atmos.washington.edu/~ovens/wxloop.cgi?mm5d2_slp+2013092900//84/3
This is our “apple.” It’s a fairly common type of storm and is probably the more likely of the two scenarios, although my opinion is starting to shift as I’m taking a look at the current water vapor imagery. Still, the GFS has been more consistent and is more in line with the Canadian model this morning.
Now, let’s take a look at the mango.
Valid 08:00 pm PDT, Sun 29 Sep 2013 – 15hr Fcst: 1000-500mb thickness, SLP (hPa). UW MM5-NAM 12km Resolution: Initialized 12z Sun 29 Sep 2013. Retrieved from the (University of Washington) Pacific Northwest Environmental Forecasts and Observations website. Chart URL: http://www.atmos.washington.edu/~ovens/wxloop.cgi?mm5d2_e_thick+//72/3.
The NAM paints a much more dire scenario for Western Washington, particularly Puget Sound. An intense low moves to Cape Flattery and deepens to an astounding 966 millibars before steamrolling through southern BC. This would give damaging winds to all of Western Washington. 
But at this point, these models don’t much matter. Our best sources of information are the satellite images offshore, especially the water vapor models. When a low pressure system is undergoing explosive development as this one is right now, a “dry slot” – an area of relatively dry air at the center of the low – begins to become larger. This often does not show up on the visible or infrared satellite imagery. Take a look at the water vapor image below and you’ll see what I mean.
http://sat.wrh.noaa.gov/satellite/alternative.php?wfo=pqr&area=nw&type=wv&size=4
See how is that little slot of black and red? That marks the center of the low. The region of moisture north of this slot is what is called the “bent-back occlusion” and is indicative of a meteorological “bomb” – an explosively developing and deepening mid-latitude cyclone. Check out this link to watch this animation. You can bet that I’ll be watching this loop all day.
The National Weather Service, which was hesitant to give King County a High Wind Warning, has now given one to them and has upgraded the Wind Advisory in Pierce Country to a High Wind Warning as well.

God… this is next to impossible to write when listening to Steve Raible call the Seahawks game. That’s why it’s two hours later and I’ve only gotten this far.

But this is enough for now. The bottom line is that we will have to watch the satellite. Also, now that we have the coastal radar at Langley Hill, we will be able to get a better idea of the location of the low. If the NAM is correct, Western Washington will see the most damaging wind event in several years… perhaps the strongest since the Hanukkah Eve Storm of 2006. It’s a very exciting time for meteorological maniacs like me.

Enjoy your Sunday! Stay posted… I’ll post updates as new details come along.

Chaz

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