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Five tornadoes were confirmed by the National Weather Service in Sioux Falls as a result of severe thunderstorms that moved through northwest Iowa on Thursday, May 1, 2008.

A long track, EF2 tornado, initially touched down 4 miles south of Rock Valley, Iowa at approximately 7 PM CDT.  This tornado remained on the ground for nearly 25 minutes, finally dissipating 2 miles east-southeast of Inwood, Iowa.  EF2 winds are estimated to range from 111 to 135 mph.  A map of the tornado path as well as a specific description of the damage is below.

The tornado path length was nearly 13 miles long, passing just west of Rock Valley, doing damage at an industrial park on the western edge of the town.  Based on the debris path the tornado was approximately one quarter mile wide when it was south of Rock Valley.  As it passed Rock Valley and moved to the northwest, the tornado was estimated to range from 300 to 500 feet wide.

At least 8 farmsteads along the tornado path sustained varying amounts of structural damage, along with heavily damaged shelter belt trees.  Numerous power poles along the tornado path were also sheared off or toppled.

This storm was rated EF2 on damage observed primarily west of Rock Valley.  The Enhanced Fujita scale ranges from EF0, 65 to 85 mph winds, to EF5 with winds estimated in excess of 200 mph.

Four other tornadoes, all rated EF0, 65 to 85 mph winds, were confirmed at:

  • 2 miles east of Doon
  • 2 miles west of George
  • 4 miles southwest of Sioux Center
  • 3 miles south of Sheldon

Below is the overview of the path of the tornado that moved near Rock Valley and Inwood, Iowa.
Overview of the path of the Rock Valley and Inwood tornado from May 1, 2008

The tornado touched down around 7 pm 4 miles south of Rock Valley.  The tornado quickly strengthened to EF1 as it moved to the north-northwest at 35 mph.  As it crossed 330th Street, it had strengthened to EF2 and was approximately 1/4 mile wide.

The tornado then moved just west of Rock Valley, Iowa around 7:07 pm CDT.  As it moved through, it was estimated to be 300 to 500 feet wide and had a rating of EF2 along most of its path near Rock Valley.

The tornado continued to move north and weakened for a brief period.  It was rated EF0 as it approached Lyon County.  However, as it moved toward Inwood, it strengthened to EF1 around 7:20 pm CDT and approached a farmstead 2.5 miles east-southeast of Inwood.  After moving northwest of the farmstead, the tornado quickly weakened and dissipated around 7:25 pm 2 miles east of Inwood.