NWS Louisville reflectivity images of supercell thunderstorms over Hardin, northern Hart, and western Larue counties in central Kentucky on January 2, 2006. The radar is at Ft. Knox at the top of the images. Heavy rain and hail occurred from many of the storms. A tornado also developed from the cell in central Hardin. The storm was non-tornadic in the far left image, but a short time later had a tornado on the ground at the small red dot in the storm's hook echo near Rineyville (near left image).
This event occurred in early January. Severe weather and tornadoes can occur in any month of the year across the Ohio Valley, and is referred to as "cool season severe weather." If enough warm, moist air is drawn northward from the Gulf of Mexico ahead of a strong low pressure system to the west, then severe storms can erupt which are supported by moderate or strong wind shear in the atmosphere.