Hail and Damaging Winds in Iowa, July 1, 1994

A cold front moved southeast out of the Dakotas into Iowa during the late afternoon and evening hours. Parameters for severe weather were weak. The instability was there, but moisture, inflow, and shear were marginal. A mesoscale convective system developed over Minnesota during the afternoon hours. As the evening progressed, the storms developed toward the southwest. Eventually the complex overspread about the northeast two thirds of Iowa. Some severe weather was reported with the storms, but it was limited. Since the storms occurred across the midnight hour, a few reports were included in the June Storm Data. Dime-size and slightly larger hail fell in west central Iowa after the midnight hour. Minor damage occurred in Arthur as one storm produced winds of nearly 60 MPH. High winds in the Ida Grove area caused damage to two homes there as trees were toppled onto the houses. There were other spotty reports of winds near 60 MPH from around the state, but they were quite isolated. The storms continued east and south across the state during the night, but the system had transformed from a severe weather producer to a general rain event. Urban flooding occurred in parts of Ida County. Local street flooding in Ida Grove was as high as the car bumpers. As the thunderstorms moved across Des Moines, lightning struck one of the buildings downtown. The Equitable Insurance Building was struck by lightning on the 20th floor. A decorative block was shattered and fell to the ground. Lightning struck a tree in Manson. A large branch was broken off and fell through the second floor window of a house there. Minor roof damage was reported in addition to the broken window.

A very unstable airmass was over the central plains during the late afternoon hours. Lifted indices were in the -10 to -12 °C. range with convective available potential energy values around 5000 J-Kg-1. During the day, a weak cold front sank slowly south across Iowa. By the late afternoon hours it had become stationary along the southern Iowa border, extending into southern Nebraska. A fairly strong southerly flow of moist air impinged on the front during the late afternoon and evening hours. This aided in the formation of a mesoscale convective complex. Iowa was on the far northeast edge of the complex and thus severe weather was somewhat limited. There were reports of hail and high winds over the southwest quarter of Iowa. Much of the severe weather was over the extreme southwest counties. Hail was under an inch in diameter, while wind gusts were generally around 60 MPH with the stronger storms. During the middle evening hours, gusty winds developed over the northwest and west central counties of the state. It is believed these winds were the result of a rear inflow jet on the back side of the mesoscale convective complex. Winds profiler data tended to support this idea and fit with literature written on the subject. The winds blew from the east to southeast at 40 to 50 MPH at Sioux City and Little Sioux for about 2 hours. Winds returned to normal by midnight.