Flash Flood in Boone County, Iowa

Water flowing through the grounds of Boone Speedway.

Two rounds of convection moved across Iowa in quick succession beginning in the pre-dawn hours of July 12th. This first was an area of convection that developed along an elevated boundary into northwest Iowa. While this area of storms mainly remained sub-severe, severe hail did fall across central Iowa near 6 am. At the same time a MCS moved out of the Dakotas and into western Iowa, moving quickly and eventually merging with the first area of storms. This second round developed into a line of storms with winds gusting up to 70 mph, fueled by the low level jet. Orientation of 0-3 km shear was favorable for quick spin-ups and two weaker tornadoes did form in Cass county that morning. With deep warm cloud layers over 4000 meters and precipitable water nearing 2, areas that received rain in both rounds received two to four inches by the time storms ended late in the morning. An isolated pocket of four to six inches fell in Greene and Boone counties, creating flash flooding in the area.