Sequential Images Of April 9 Tornadic Circulation

When our storm chase team members were on-the-spot witnesses to this set of scenes about five miles southeast of Mapleton, Iowa around 7:30 PM, Saturday, April 9, 2011, we weren't totally sure if what we were actually seeing was a tornado or not. The structure was dust and rain-wrapped--with darkness falling--adding to our difficulty of making out much inside the churning mass of clouds. Also confounding us at this particular moment was the perceived lack of confirmed reports from spotters and Emergency Management personnel in the Mapleton area. As it turned out, my camera was much better at discerning the circulation than were our naked eyes. A passing motorist had pulled up alongside us earlier and told us he had heard of "two tornadoes on the ground at Mapleton." Confirmation of a single (EF3) twister came later and the town suffered damage to about 60% of its area as a result of this storm. After reviewing the video in which these images came from, we are now convinced that this circulation may actually be an RFD (Rear Flank Downdraft)-induced anticyclonic "flare." Its location and time does not match up with the main vortex, which would have been farther NE, and the main vortex spun cyclonically, leading us to this conclusion. These four video frame image captures were taken at the connector bend of Sumac Avenue (foreground) and 170th Street (background). The lower right image shows a satellite funnel protruding from the left side of the main vortex structure.