Wednesday, December 10, 2014

Major Windstorm Tomorrow?

Wednesday, December 10, 2014
12:30 pm

I've got one more final tomorrow at 11:30 am, but here I am, blogging away my anxiety. Why on Earth would I put 40% of my grade on the line to write a stupid weather blog (and yes, I'm going to need all the time I have to study for this test. Kids, beware of atmospheric motions 441.)?

Because we might see a major windstorm tomorrow. 

Now, this isn't going to be a catastrophic windstorm for the Puget Sound lowlands, at least not at this point. Believe it or not, there were a couple models that were advertising that it could be. I define a "catastrophic windstorm" to be a storm with widespread gusts to 60-70 mph in our region. While that may not be a lot for the coast, it's a pretty big deal for the inland areas west of the Cascades. And with our saturated soils and excess of giant evergreens, you can bet that 60-70 mile per hour winds here are going to cause a lot more damage than equivalent winds in the Great Plains or even New York City. I would say our last catastrophic storm was the Hanukkah Eve Storm of 2006. This storm doesn't look to equal that one in magnitude for our region, but it could be one of the strongest since then. It could be. 

Why all the uncertainty? The storm is 24 hours out, so shouldn't we be smart enough to know if we're all going to die a grisly death? Well, the answer is yes, but the reality is no. The models have been inconsistent with the storm, but honestly, that's not the biggest problem. It's the very nature of the storm that were dealing with.

You know those Nor'easters they get on the East Coast? Well, this is its Northwestern cousin, the "Sou'wester." These are the storms that are historically the most damaging storms to our area, and they tend to impact the entire west coast. The last really big one was in December 1995, creating gusts of 72 mph from Cape Mendocino, CA to 76 mph up in Bellingham, WA. Portland hit 74, Sea-Tac hit 60, and Mukilteo, just to the north of Seattle, hit 86. And Cannon Beach, Newport, and Sea Lion Caves on the Oregon Coast all hit well above 100 mph.

The Columbus Day Storm of 1962 was also a Sou'wester, and any Pacific Northwest weather aficionado is familiar with "The Big Blow." With 179 mph winds at Cape Blanco, 116 mph winds in Portland, 127 in Corvallis, 100 in Redmond... you get the point. The Columbus Day Storm was the David Banner of Pacific Northwest windstorms, and we likely will not see one like it for hundreds of years. All these diagrams were taken from Wolf Read's The Storm King website.

I'd love to go on and on about massive Sou'westers, but you get the point. These are the big storms. They typically form south of Eureka around 135 West, and from there, they rapidly intensify and curl northward. Depending on how close they get to the coast, they can bring strong winds to an extremely large area. The Columbus Day Storm nearly paralleled the coast from California to Vancouver Island and remained just offshore, giving all areas a tremendous blow. Conversely, the Hanukka Eve storm came from the WSW and crossed Vancouver Island, only delivering its main blow to Washington as it never got close enough to the California and Oregon coasts for them to feel the full effect. Take a look at the pics below and notice the difference in tracks.

You can see how the Columbus Day Storm would have impacted a much wider area. Additionally, it was much deeper, so that contributed to the breadth and magnitude of destruction. AND, it occurred, on, well, Columbus Day, when many trees still had their leaves. Truly a worst-case scenario for destruction, yet a fascinating one from a meteorological point of view.

Now that you have a little background on Sou'westers, let's get back to talking about our forecast. As the track from the Columbus Day Storm shows, even a slight displacement to the west would have weakened the winds significantly across the region. Storms like the Hanukkah Eve Storm shown above that smash into southern Vancouver Island from the SW are not nearly as sensitive to changes in track. That's what makes this forecast so hard. Tiny changes in track with these types of storms mean major changes in effects. Remind you of another type of forecast here? (hint: it starts with an 's'). The National Weather Service sums this up well with their latest "weather story."

This specific storm has changed wobbled from making a direct pass right over Seattle to passing right off our coast, sparing us major winds. It will not even approach the Columbus Day Storm, and it will not be as strong as the Hanukkah Eve Storm even in a worst case scenario. The storm itself has a much higher pressure than the CDS; it bottoms out at around 970 off of the Californian Coast, and then it slowly weakens as it travels northward. Let's compare some previous model runs just so ya'll know what I'm talking about.

Here are the two most recent model runs from the UW. Last night's is below, and this morning's is below that.

Valid 01:00 pm PST, Thu 11 Dec 2014 - 45hr Fcst - Retrieved from UW mm5rt

Valid 01:00 pm PST, Thu 11 Dec 2014 - 33hr Fcst - Retrieved from UW mm5rt

You can see that the low this morning is further south (it is arriving later), weaker, and further offshore (this becomes even more apparent during later slides). However, I just checked the European model, and it is slightly closer with the low.

Credit: Weather Underground

Additionally, I just checked the latest 18z GFS, and it is ever so slightly closer with the low, although still offshore.

The bottom line:

I don't think this will be a major event for the Puget Sound lowlands. It will get windy, and there will be power outages. But I don't expect this to be a widespread, damaging event. The main reason is that regardless of the track, the low looks to be weakening too quickly as it heads up north.

However, as I said before, tiny changes will have big effects. We have a high wind watch over our area.

OK, NOW it's time to study. I might make a webcast tonight if I get some stuff done. Maybe.


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