By James Baughn
I did a double-take when I saw this morning's radar image:
Did a hurricane suddenly form over Missouri? The huge area of storms over most of Missouri certainly resembled a tropical system, complete with "spiral bands" and lots of reds and oranges on the radar.
As the morning wore on, the system was clearly rotating around an "eye":
Of course, this wasn't actually a tropical system. This type of thunderstorm complex is called a "derecho." When the National Weather Service issued their Tornado Watch this morning, they explained:
A MATURE VERY INTENSE DERECHO IS MOVING VERY RAPIDLY ALONG THERMAL/INSTABILITY GRADIENT ACROSS MID MS VLY INTO TN AND LOWER OH VALLEYS. WITH A VERY MOIST UNSTABLE AIR MASS AND STRONG VEERING SHEAR PROFILES...EMBEDDED TORNADIC SUPERCELLS WILL CONTINUE TO BE ASSOCIATED WITH THE DERECHO ALONG WITH WIDESPREAD DAMAGING WINDS.
The Storm Prediction Center defines a derecho
as a "widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms." Their Derecho Fact Sheet
offers more information than you probably wanted to know.
While these storms are sometimes called inland hurricanes, they are not tropical at all. Nevertheless, these things can easily cause hurricane-force damage, as we now know.