Saturday, October 25, 2014

Windstorm on the Way

Saturday, October 25, 2014
1:12 p.m.

First off, sorry for not being the most punctual poster as of late. I was actually recently contacted by the University of North Carolina of all places to write a weather blog using some of their graphics for WeatherOn. I really hope it will put uss "On" the map. Get it? :D

Anyway, you can check out the blog I wrote here.

But that post can be read anytime. We've got some action coming in right as I type this sentence, and things are starting to look pretty hairy around the Pacific Northwest.

Earlier this week, there was some talk about a windstorm impacting Oregon and Washington. This windstorm had the classic track of a "Sou'wester," (compare to Nor'easter) which is the slang term for the biggest region-wide windstorms we get in the Pacific Northwest, as they often come out of the southwest.

Image Credit: OWSC: Wolf Read's Storm King Website

We haven't had too many of these big Sou'westers lately. Our last one of note was January 16, 2000, but our last really big one was December 12, 1995. We had another big one back on November 13, 1981 as well. Still, none of these can compare to the granddaddy off all sou'westers, and in fact, the strongest extratropical storm to ever hit the United States: the Columbus Day storm of October 12, 1962. Some call it the CDS, some call it simply "The Big Blow," and others, like myself, prefer the unnecessarily verbose "Terrible Tempest the Twelveth." Either way, the Columbus Day Storm was a sou'wester on a whole other level, and a storm a likes of which we will not see for centuries, even millennium. It truly was a singularity, and it still casts a dark shadow over every other single storm to hit the Pacific Northwest. Many of them have been very memorable, but none of them have caused such widespread destruction over such a wide area. I would give an arm and a leg to see what that beast looked like on satellite, but alas, there were no satellite shots taken of it. The sad thing is that I'm not necessarily joking when I say I'd give an arm and a leg... I'd just be taking one for the team. I'd have to ponder over it.

You'll notice that two of Seattle's largest windstorms - the Inaugural Day Windstorm of 1993, and the Hanukkah Eve Storm of 2006, are not listed. The reason for this is that they are not sou'westers in the first place. They approached the coast from a more western track instead of paralleling the coastline. If they did parallel the coastline, they would have impacted a much larger amount of inhabited land, and the damage totals would have been much higher.

The three major cyclones I just mentioned - 1962, 1981, and 1995, were all below 960 mb, which is about equivalent to the pressure of a category 3 hurricane. This cyclone is predicted to drop to around 985 mb. Accordingly, the winds will be much less, but it has already taken a track of a region-wide windstorm and affected a large area, and it is on a course to provide particularly high winds to the Seattle metro area as it passes just to the north of it. Winds are already picking up here right now.

Take a look at the rooftop data from the UW atmospheric sciences building. In particular, take note of now the winds have strongly increased just in the past hour. And folks, they are only going to get stronger.

Atmospheric Sciences Building 24-hour rooftop summary

Taking a look at our current satellite, you can see that the low pressure is just starting to make landfall into Western Washington. Oregon is still seeing strong winds, but the strongest ones are likely over. Winds will hang on a little longer in northern Oregon.

5pm UW Infrared Satellite

Additionally, here are the warnings and watches in effect for Western Washington and Western Oregon. It's not often that you see tan in the Puget Sound area, especially in October.

NWS Seattle

NWS Portland

The effects of this windstorm could be exaggerated by the fact that the deciduous trees still have the majority of their leaves on them (at least they do right now!). More leaves = more surface area, and a higher surface area will catch more of the force of the wind gusts and transfer that force to the tree, making it more likely to snap or topple. In addition, our soil is relatively saturated due to that massive rainstorm we saw earlier this week, and since saturated soil loses its cohesion, it is easier for complete tree failures to occur in the presence of it. As if all this wasn't enough, there have been weak and dead branches that have stayed in the trees all summer long, and being the first windstorm of the season, this one is the one that is most likely to blow them all off. Don't be startled if you lose your power tonight.

Thank you! Stay safe!

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