EF1 tornado in Marshall County, Iowa

This is a multiple segment tornado with three segments that passed through portions of Story, Marshall and Hardin counties. This is the second segment in Marshall county. After turning to the east and entering Marshall County, the tornado rapidly widened and intensified just after crossing County Highway S57. Severe damage occurred to a 500 yard wide stretch of trees along Minerva Creek along and north of 120th St. (part of the damage was likely attributable to RFD). The tornado continued east just north of 120th St. and completely destroyed a farm outbuilding, depositing the remnants of the building in the surrounding trees to the north and east. Very strong RFD winds caused widespread tree and building damage for over a mile south of the tornado path along this section of the track. Turning northeast, the tornado tracked across open farmland for the next 2.5 miles, grazing one farmstead in the process. The narrowing tornado directly hit a farmstead south of the 105th St. and Fariman Ave. intersection, with mostly low EF1 tree damage sustained. The tornado then continued into Hardin county.

A very dynamic pattern was in place over the state with a closed low located over southern Canada into the north central U.S. A very strong jet of 85 to 100 kts as present at 250 mb. CAPE by early morning was already 3000 to 4000 J/kg with downdraft CAPE of 1000 to 1400 J/kg. CAPE in the -10 to -30 C layer of the atmosphere was between 1000 and 1400 J/kg. The freezing level was around 14,000 feet with precipitable water values near 2 inches. The LCL remained around 750 meters with 75 J/kg of CAPE in the 0-3 km layer. There was strong shear present, with 60-80 kts of effective shear. A cold front moved into Iowa during the day and moved across the state. This event was similar to the event of 29 June 1998. Thunderstorms formed over northeast Nebraska by sunrise and continued to propagate east into Iowa. The storms intensified as they moved across the state, into a forward moving MCS. As it strengthened into a Derecho, winds of 70 to 80 MPH were reported over a large swath of the state. All modes of severe weather occurred. Widespread wind damage was reported to trees, power lines, and structures from the high winds. In addition, very large hail occurred. Some of the larger hail included three to four inch diameter hail in Calhoun County near Rockwell City, and three and one half inch diameter hail in Warren County at Sandyville. Several tornadoes were confirmed. Very heavy rainfall occurred with the storms. The rain lead to flooding and flash flooding in many areas of northern and central Iowa. By the end of the month, a presidential disaster declaration had been made for the follow 9 Iowa counties: Adams, Clarke, Decatur, Mills, Montgomery, Pottawattamie, Ringgold, Taylor and Wayne. Governor Branstad also requested a disaster declaration for the following 26 Iowa Counties: Allamakee, Buchanan, Buena Vista, Butler, Cherokee, Chickasaw, Clay, Dickinson, Emmet, Fayette, Franklin, Hancock, Humboldt, Ida, Kossuth, Lyon, Osceola, Palo Alto, Plymouth, Pocahontas, Sac, Sioux, Winnebago, Winneshiek, Woodbury, and Wright. The Presidential declaration was granted on 24 July 2014.