This is only the second EF-5 ever in the U.S. (the other one was the infamous Greensburg,KS) Here's what the Quick Responce Team from the Des Moines NWS in Iowa found on its investigation. Article from NWS in Des Moines.
Parkersburg Tornado Rated a Low-end EF5
Last updated at 4:30 p.m. Tues. May 27, 2008
SummaryNWS personnel have rated the Parkersburg-New Hartford-Dunkerton tornado as a Low-end EF 5 (correlated to wind speeds up to 205 MPH) on the Enhanced Fujita Scale at the locations of maximum damage. Additional details on path length, width, etc. will be posted on this webpage Wednesday, May 28. This is the first EF5 tornado in Iowa since the Jordan tornado of June 13, 1976.A large and destructive tornado moved across Butler and Black Hawk counties on Sunday May 25th. The initial touchdown occurred near the Butler and Grundy county line, 2 miles south of Aplington at 4:48 pm CDT and quickly grew in size and intensity as it approached Parkersburg. The tornado was nearly 3/4s of a mile wide as it moved through the southern end of Parkersburg at 4:59 pm CDT. Significant structural damage occurred in the town of Parkersburg including 100 to 200 homes destroyed. The tornado maintained size and intensity as it move towards New Hartford. At 5:09 pm CDT the storm moved just north of New Hartford once again causing significant structural and tree damage. The tornado weakened around 3 miles east of New Hartford with lesser damage as it moved east to north of the Waterloo and Cedar Falls area. Significant straight line winds occurred along and just south of the tornado track with preliminary estimates of 90 to 100 mph. The tornado then grew in size to near 1.2 miles wide north of Dunkerton causing substantial damage to a farmstead there. The tornado lifted just before entering Buchanan county.