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This loop of GOES-8 3.9 micron shortwave InfraRed imagery shows the swath of wet ground left behind in the wake of the early morning convection that moved through the region. The wet ground is delineated by cooler brightness temperatures (lighter gray enhancement) early in the loop over northwestern Iowa/southwestern Minnesota, and late in the loop over northeastern Nebraska. Counties in southeastern South Dakota with preliminary tornado reports (from west to east: Davison, Hanson, McCook, and Turner) are outlined in blue, and Spencer is located in extreme western McCook county.
Differential heating along the wet ground - dry ground boundary may have played a role in the movement and intensification of the supercell convection that formed later that evening and affected the outlined counties.