Iowa tornadoes: 12 twisters confirmed within 24 hours By Stephanie Weaver Iowa woman has brush with twister during severe storm The National Weather Service issued multiple tornado warnings as a line of storms moved through central Iowa on July 14. (Credit: Emma Corbin via Storyful) DES MOINES, Iowa - A night of severe and dangerous storms Wednesday spawned 12 confirmed tornadoes in Iowa and more than two dozen reports of possible twisters in the state, according to the National Weather Service. The NWS said supercells developed over central Iowa during the afternoon on July 14. "The environment was ripe for tornadic development and rotation was evident on radar shortly after storms formed," NWS reported.