A large thunderstorm complex formed over southeast Kansas early Fridaymorning. This complex moved east and created a swath of damaging winds, hailand heavy rain across southern Missouri, northern Arkansas, southern Illinois,northern Kentucky and extreme southern Indiana. This large thunderstorm complexformed along a surface boundary separating super warm moist air moving up fromthe south from drier and cooler air to the north. This boundary was roughlyfrom southeast Kansas to just south of the Ohio River. A strong southerly flowof air about 3000 feet above the surface from the Gulf of Mexico transportedwarm moist air into this boundary. This flow of lower level air is oftenreferred as a "low level wind jet". As this wind flow increased early Fridaymorning an upper level disturbance tracking east from the south central Rockiesstarted to cause the atmosphere to become more unstable. The upper level systemalso caused winds above this low level wind jet to turn more out of thesouthwest. This caused the winds flowing into this feature to spiral into andaround the center of the complex. This wind shear is what caused somedeveloping thunderstorms to rotate. The interaction of this upper leveldisturbance, the low level wind jet and the surface boundary created theingredients which lead to the development of this large and destructivethunderstorm complex.The development of these thunderstorm complexes are not unusual, especiallythis time of the year. But what made this thunderstorm complex so unique wasthe size and the evolution of a large bowing line of damaging thunderstorms.
When thunderstorms rotate the shape of of the clouds, wind and rain bow outmaking them damaging wind producers. When a group of rotating thunderstorms bowoutward a large damaging wind storm develops. That is what happened today. Thebowing line of thunderstorms moved so fast that a part of the thunderstormcomplex wrapped around the upper level disturbance that helped to create it.
The thunderstorm complex became a massive comma shaped area of destructionincluding the formation of fast moving tornadoes. This does not happen veryoften. In fact the size and shape of this destructive thunderstorm complexmight only occur once in every 10 to maybe 20 years.
In its wake there were over 150 reports of wind damage, at least 11 reportsof tornadoes and 39 reports of hail. Many of the damaging wind reportsreached speeds of 80 to 90 mph. Carbondale Illinois reported a wind gust of106 mph. These phenomenal wind reports caused some meteorologists and weatherenthusiasts to call this damaging wind producer as an "inland hurricane".
However, many researchers call these damaging wind complexes "derechoes". Aderecho is defined as a widespread convectively induced wind storm within amesoscale convective system covering a path ofcreating a chronological and nearly continuous area of damage for at least 3straight hours. This damaging thunderstorm complex created a path ofdestruction covering well over 350 nautical miles in a span of over 9 hours.
Regardless of what you call it this destructive thunderstorm complex it willweaken as it moves into the Appalachians Friday night transitioning from adamaging wind producer to a flooding rain producer. Let us hope we do not seeanother destructive weather disturbance like this for quite some time.
By AccuWeather.com Expert Senior Meteorologist Dan Kottlowski
