Monday, September 10, 2012

Downbursts are Dangerous

Via Twitter.
Jamie is replying to a tweet from the Washington Post's Ian Livingston about the National Weather Service's findings that a tornado did not occur Saturday in the DC area. And, throughout my career, I've found the same thing: People often feel let down when damage is determined to have been caused by straight line (SL) winds than a tornado.

But, thunderstorm straight winds can be damaging, dangerous, and even fatal as Friday in Oklahoma demonstrated. 

I was attending a working seminar southwest of downtown Oklahoma City when I heard the GPS weather alarm go off on my cell phone indicating we were in a severe thunderstorm warning. About five minutes later, thunder so loud it shook the meeting room reverberated through the air.

I'm at the blue symbol when the downburst lowered to the ground at 3:18pm
The yellow polygon is a severe thunderstorm warning that was already in effect. 
That thunder was a result of the cloud-to-ground lightning that usually occurs when a downburst is lowering to the ground. Within moments, high winds were occurring at the hotel that I estimated up to 60 or even 65 mph.  It is hard to tell in the photo but it was pouring.

The Doppler wind portion of the radar data a eight minutes later showed a strong downburst. In a downburst, the winds blow outward from a central point. Keep in mind the radar can sense winds blowing away from the radar (red) and toward the radar (green). Winds blowing perpendicular to the radar, no matter how strong, are not sensed. At this time, the peak wind sensed by radar was 60 mph; those later increased to about 70 mph.

As the downburst winds moved east with the parent thunderstorm, it moved over the weather station at Tinker Air Force Base near Del City (at right on image above) where a wind gust of 76 mph was recorded at 3:56pm CDT. This type of storm used to routinely cause the crash of commercial airliners but that problem has largely been solved thanks to weather science.

In Oklahoma City, there were trees and powerlines downed. Our power briefly failed. But, that was the extent of the issues. In northeast Oklahoma, it was a tragically different story.
At the same time the high winds were occurring at our hotel, three were killed when a downburst destroyed their mobile home near Nowata, Oklahoma.
KJRH TV screen capture image via Yahoo
Downbursts are capable of doing major damage. If you live in a mobile home -- especially if it is not tied down -- you need to seek other shelter when a severe thunderstorm warning for high winds is issued.  

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