Anatomy Of A Mesocyclone

This rotating meso was made visible only because of the flash of lightning and an extended exposure of about 10 seconds as the hour was about 9:35 PM, Saturday, April 9, 2011. The structure is left (west) of County Road N33, about 1.5 miles west of Knoke, Iowa. Because of darkness, its rotation was apparent only by clicking on successive individual images in Photoshop. The meso was part of a powerful storm that moved through western Iowa that Saturday evening--influenced by high instability and wind shear--and produced many tornadoes. Inflow bands are seen just above the darker lower portion. A lowering in this image that may have produced a tornado later is hidden by the farm at left. A mesocyclone is a cyclone intermediate in size (2-6 miles in diameter) produced by a supercell thunderstorm and is the intense rotating updraft portion of that storm. Very strong RFD winds (40-50 mph) made keeping this image in focus very difficult! (What a difference a week makes in Iowa: temperatures on April 9 were in the lower 80s, and exactly one week later temps were in the upper 30s with snow showers!)