As of this writing, three tornadoes rated EF-2 (Enhanced Fujita scale) and three rated EF-1 struck the Ozarks overnight Tuesday into early Wednesday.
The EF scale goes from 0-5 with 5 being the most violent. Tornadoes rated EF-2 have estimated winds between 111-135 mph. EF-1 tornadoes rank in the 86-110 mph range.
-Kimberling City to Branson
-Northwest of Cassville in Barry County
-Southwest of Buffalo (Polk and Dallas Counties)
-Near Greenfield to Near Aldrich (Dade to Polk Counties)
-Near Bennet Spring
-Phillipsburg to Lebanon
Why Did These Tornadoes Occur?
The atmosphere over the Ozarks during this time was characterized by a very strong field of winds extending deep through the atmosphere.
The jet stream winds, those found higher up in the atmosphere, were fast, around 100 miles per hour just to the north of the Ozarks! This is what accounted for the amazing speed of the thunderstorms which was anywhere between 50 and 70 mph Tuesday night. Strong winds like this also help in the formation of supercell thunderstorms, those which are able to sustain themselves for longer periods of time.
The wind near the ground was the real story during this tornado outbreak. The proper low level winds encourage thunderstorms to rotate. If the winds right near the ground are just right, tornadoes will form. The low level winds where extremely conducive to the formation of tornadoes that night! Generally you want winds which increase speed rapidly with increasing height and for those winds to turn more out of the west as they do so.
Finally, there’s the idea of unstable air. A thunderstorm needs at least some instability for an updraft of air to form. While the instability in place wasn’t high compared to spring and summer values, it was more than enough to put the storms “on the map” so to speak. After that, with the winds described, it was very easy for storms to acquire rotation.