Heavy Rolling In Near Onawa

The overhanging anvil of a building supercell rolls into the state of Iowa from Nebraska just before 6:00 PM, Saturday, April 9, 2011. This spot on Cherry Avenue (a dirt road) just .1-mile south of Highway 175 (background) was our second storm initiation waiting point for the day's chase and is located about 2.8 miles west of the Onawa, Iowa exit (Exit 112) from Interstate 29 or about one mile southwest of Lewis and Clark State Park. The image looks northwest. The powerful supercell began forming in eastern Nebraska just after 5:00 PM and by about 7:15 PM, it dropped its first tornado just southwest of Mapleton, Iowa--17.5 miles northeast of here. The tornado would later be rated an EF3, and damaged a large portion of the town around 7:30 PM. Many more tornadoes also formed from the system as it moved farther to the northeast. Unseasonably warm temperatures (81 degrees) and high dew points (73 degrees) on this day in western Iowa helped fuel the instability of the atmosphere.