Hail and Damaging Winds in Iowa, July 14 to 15, 1998

A very unstable airmass was located over Iowa the afternoon temperatures near 90 degrees F. and dewpoint temperatures in the low 70s. A cold front was located well to the north of the state across North Dakota and northern Minnesota. During the late afternoon and evening hours, thunderstorms fired along the cold frontal boundary. The storms initially moved east, but the entire line began sinking slowly south during the early evening. The flow aloft was northwest as Iowa was on the east side of a large upper level ridge of high pressure located in the southern and central Rockies. During the late evening hours, the line of thunderstorms turned nearly due south and advanced into Iowa. The event turned into a Derecho event as the line bowed south into the state. The first reports came from the far northern counties were high winds took the roof off of a house in Emmet County at Wallingford. Trees were downed in many areas from northwest, north central, into parts of central Iowa. Winds of 90 MPH were recorded in Winnebago County northwest of Scarville, with numerous reports of winds near 70 MPH as the storms moved south. A semi-tractortrailer truck was tipped over east of Goodell in Hancock County by the high winds. As the storms moved through the Algona area in Kossuth County, high winds did $10,000 to $15,000 damage at a golf course there. Winds lifted and destroyed two sheds there. Though some small hail was reported with many of the storms, very little of it was in the severe category. Golf ball size hail did fall in Crawford County at Denison however. The storm weakened rapidly once the approached central Iowa, however the line did move south well into Missouri by sunrise. The outflow boundary swept across much of the northwest and north central parts of Iowa. The reports mentioned above were from confirmed reports, however news reports indicate that vast areas of these counties were affected with widespread crop damage. Thousands of acres of corn and soy beans were flattened by the high winds with damage in the millions of dollars. The corn was quite susceptible to damage due to where it was in the growing stage. Much of the damage was due to what is known as "green snap". Green snap is caused when high winds hit corn that is in a very rapid stage of its growth. Because of the high water content in the plant, is tends to break off more easily at this point in the growth cycle.