High shear low instability tornadic storm

Yesterday, January 11, there was a somewhat unusal and unexpected tornadic storm in Virginia. The F1 tornado injured two people and damaged several mobile homes.

http://www.wavy.com/Global/story.asp?S=4353214

http://www.spc.noaa.gov/climo/reports/060111_rpts.html

The tornado occurred with the approach of a cold front at approximately 6:30PM. Winds in that area briefly became backed and there was strong shear according to the SPC mesoanalysis. The storm was tornado-warned but there was no early indication (tornado watch, SPC slight risk etc.)

Nearest surface obs (West Point airport)

Temp Dewpoint
8 PM (1) Jan 11 59 (15) 57 (14) 30.02 (1016) SW 6
7 PM (0) Jan 11 57 (14) 57 (14) 30.01 (1016) S 5
6 PM (23) Jan 11 57 (14) 57 (14) 30.03 (1016) SSE 5
5 PM (22) Jan 11 60 (16) 57 (14) 30.02 (1016) SSE 9
4 PM (21) Jan 11 64 (18 ) 55 (13) 30.05 (1017) SSW 8
3 PM (20) Jan 11 66 (19) 55 (13) 30.05 (1017) SSW 5

This unexpected situation shows the wide range of shear/instability conbinations that can cause tornado formation. In this case, there was high shear and almost nonexistant instability.

Bill Hark
http://www.harkphoto.com

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