Tornadoes and Flooding in Iowa, May 30, 2000

An explosive situation became established over Iowa and the central U.S. during the day on the 30th. A nearly stationary front extended from Wisconsin, southwest through the northwest corner of Iowa, and into northern Kansas. A round of convection moved across the state during the morning, leaving behind several outflow boundaries. The mid levels of the atmosphere were quite warm, thus convection was capped during the afternoon hours. A strong southerly flow of moist air spread into Iowa during the afternoon. Temperatures approached 100 degrees F. over southwest Iowa. Dew point temperatures reached the upper 60s to mid 70s across much of the south two thirds of the state. Thunderstorms developed at the intersection of two outflow boundaries northwest of Des Moines, and also just ahead of the stationary front. Surface based CAPE values were well over 5000 J/kg, thus the convection developed explosively. Severe weather quickly followed. There were numerous reports of hail. Most of the hail was between one inch in diameter and golf ball size. One of the cells, which happened to be the initial cell that formed at the boundary intersection, turned into a supercell. Several tornadoes were spawned by this regenerating cell. Most of the tornadoes were very weak and short lived. The exception was one fairly small tornado that touched down on the northeast side of Des Moines. This tornado tracked through mostly open area and caused little damage on its nearly 10 mile intermittent trek into Altoona. Gusty winds were reported with many of the cells, however wind speeds were not all that great in most cases. There was one report of 60 MPH winds as the storms passed through the Saylorville area in Polk County. Heavy rain fell in a couple parts of the state. One was with the supercell in Polk County, the other area of heavy rain was in Black Hawk County. Rainfall amounts in parts of these two counties were in the two to four inch range, however little more than urban and small street flooding occurred due to dry soil conditions.