| Episode Narrative |
An unstable airmass remained in place across Iowa with dewpoint temperatures remaining in the upper 60s to low 70s. A nearly stationary frontal boundary was in place across the state extending from the east central counties to the southwest corner of the state. Thunderstorms erupted on the north side of the front during the evening. CAPE values were between 2000 and 4000 J/kg, with downdraft CAPE of 1100 to 1600 J/kg. The lifted index was in the -4 to -6 C range. The freezing level was quite high, though it had fallen some during the day. It was just over 14,000 feet by evening. CAPE in the -10 to -30 C layer of the atmosphere was between 300 and 700 J/kg. Moisture was drawn north over the frontal boundary by a low level jet of 25 kts. Precipitable water values increased to 1.6 to 1.9 inches. The storms produced high winds as they progressed across the state. One storm broke several 10 inch branches south of Hubbard in Hardin County. This storm continued eastward and produced strong winds as it moved through Black Hawk County. Winds were measured around 60 MPH in the Waterloo area. Another cluster of storms moved into western Iowa and spread into the central counties. Winds around 75 MPH occurred in Audubon County. The strong winds, at least 60 MPH, continued east into Guthrie County before the storms weakened. There were numerous reports of trees downed, along with power line damage. Extensive damage occurred in Hardin County as winds of 75 MPH caused crop damage, ripped part of the roof off of a machine shed, and flattened several grain bins. A classic wet microburst took place south of Hubbard as well. Winds started around 1030 PM and lasted for about 8 minutes. The damage was concentrated in an area about 2 miles south of Hubbard where 3 farms sustained major damage, and a 4th farm had more minor damage. Specifically, one farm lost 12 trees (snapped). Two trees landed on and destroyed a grain bin. Also, the west-facing machine shed door was collapsed and portions of the roof (including the roof structure itself) were blown off. The next 2 farms to the south also sustained significant damage to trees with many snapped about halfway up the trunk. The farm just to the north also lost several large trees. Based on the duration of the winds, damage to the farms, type and condition of the trees, etc., estimated winds were in the 80-85 MPH range. In terms of crops, most of these farms are growing soybeans which were flattened, and part of the corn crop was blown down. Heavy rain also was reported in Bremer County with reports of around 3 inches of rain in under 2 hours. Around 2 inches of rain fell in an hour in Black Hawk County. Lightning struck a building in Cedar Falls, setting it on fire. There were also reports of two tree fires in the city of Cedar Falls. |
