Tornadoes and Hail in Iowa, May 30, 1998

A very unstable airmass was over Iowa. In spite of the instability, the atmosphere was capped by very warm air aloft. Temperatures at the 700 mb level were between 12 degrees C and 14 degrees C. As a result, thunderstorms had a difficult time forming. The atmosphere was primed with CAPE values in the 4000 to 6000 J/kg range by late morning. Helicity values were near 300 M2/S2. One cell was able to break the cap and became severe. It was a prolific hail producer as well as spawning several tornadoes. Hail reports indicated frequent baseball size hail with a few reports to softball size and larger. The largest report was an incredible 5 inch diameter stone north of Gilbert in Story County. The damage caused was incredible. In some town, every north facing window was broken out by the hail. On one building, the hail was so large that it broke the stone tile roof in the building, smashing it into pieces. Property damage was extensive in a swath from Sac County through Marshall County. Total property damage was estimated to be well in excess of $5,000,000. In Calhoun County, the town of Lohrville was hard hit by baseball size hail. Damage in the town was estimated at $1 million as the hail knocked out windows in almost all of the 225 buildings in town. One injury was reported in Lohrville as a woman was treated for an eye injury as shards of glass flew into her eye from a car windshield broken by the hail. Crop damage was difficult to assess, but was extensive. Thousands of acres of crops were shredded by the hail. In Webster County, estimates of crop damage indicated 24,000+ acres had total crop loss and 20,000+ acres suffered 30-50% loss. Crop loss in the county was expected to be over $14 million. In addition to the crop loss, property loss was estimated at between $2 and $4 million. Many emergency managers described the hail event as the worst in 25 years in some areas to the worst they have ever seen in others. To give some idea of the severity, the hail was large enough to shatter tile roofs. Scenes of broken tiles falling off of houses were common. The hail also took a toll on wildlife. Numerous Pheasants, rabbits, and other small animals were killed by the hail, not to mention the smashed birds eggs. The thunderstorm cell itself was a classic cell on WSR-88D radar. It contained a clear hook echo and bounded weak echo region. In spite of the structure looking text book perfect, the cell had a hard time producing a tornado. Several brief touchdowns were reported from northwest of Boone to the vicinity of Boone. The cell became better organized as it moved into central Iowa. A tornado touched down in Story County and moved into Marshall County. This tornado was fairly small and had a very intermittent track. Storm chasers indicated that the tornado lifted several times during its life. Damage was limited as the tornado tracked totally across open country and caused only crop damage for the most part.