The National Weather Service made final determinations about just what weather phenomenon moved across the Houston are Thursday May16, and my best guess was correct: we had a “Derecho” - pronounced Deh-REH-cho (Spanish for “straight”).
Let me explain.
By definition, a Derecho creates straight line wind damage which extends more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length. If you look at the severe storm reports from yesterday you will see a long line of “blue dots,” or high wind reports.
There were 130 wind reports (you can imagine how many were NOT reported) and you can see those at the full site. And if, geographically, the reports with the system that moved across started in Austin and went through New Orleans then that “240-mile swath of damaging winds” definition has been met. And the wind gust definition of 58mph was easily found from Austin to New Orleans where Lakefront Airport recorded a wind gust of 82 mph. In fact, most wind gusts across Houston were easily from 70-90mph.
In addition, Derechos are tied to “bow echoes”, a term from Ted Fujita of tornado fame, necessarily formed by strong winds which hit the surface and fan out like pancake batter. You can see from yesterday’s Storm Tracker 2 radar that bow echoes were absolutely visible. I’ve drawn a blue line to help illustrate:
Climatologically, May is the MOST common month for derechos to form, and our part of Texas does statistically experience a derecho every two to four years:
If you are meteorologically inclined, you can read more about derechos from the National Weather Service. I can tell you that in my career, I have never actually been through a derecho until yesterday. As I always say, if you forecast in Houston long enough, you’ll see it all.
Bottom line: I hope you and your family are safe and my heart goes out to those that lost loved ones. Please have a safe weekend.
Frank
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