Thursday May 30th, 2013 is the 15th anniversary of the tornado that hit Spencer, SD. Based on the devastation the twister was rated F4 with winds over 200 miles an hour.

"At approximately 8:40 p.m. (all times Central Daylight Time [CDT]) on Saturday, May 30, 1998, a violent tornado struck the small town of Spencer, South Dakota. Spencer is in extreme western McCook County, about 45 miles west-northwest of Sioux Falls. The tornado killed six people, injured more than one-third of the town's 320 residents, and destroyed most of the town's 190 buildings. Damage is estimated at $18 million. The Spencer tornado (rated F4 on the Fujita Tornado Intensity Scale), was one of five tornadoes, along a nearly continuous damage track approximately 30 miles long."

Below is the map of the tracks of all the tornadoes that occured with the thunderstorm that eventually spawned the tornado that hit Spencer, SD.  Notice the tornado reached it's maximum intensity, F4, in and around the town of Spencer.  As the tornado aproached Interstate 90, it was weakening dramatically and actually lifted before crossing the Interstate.  But shortly after crossing I-90, another tornado was produced by the cyclic supercell and resulted in small stretch of F2 damage northwest of Canistota, SD.