The National Weather Service has officially declared the reported Casey, Illinois "Gustnado" as a EF0 Tornado.
The tornado occurred during a chain of Memorial Day Weekend thunder storms. The tornado touched down on 25 May 2007 between the towns of Casey and Martinsville, Illinois. (photo by Curt Coffey).
NWS had received three different photographs of the tornado, along with a detailed account by a chaser who observed the twister for 10 minutes along its 2.5 mile path. The twister was estimated to be on the ground between 14:53hrs and 15:03hrs according to eyewitnesses. This twister was approximately 30 yards wide and stayed in open fields the whole time.
According to NWS, between eyewitness accounts, photos and radar data at the time, showed it was clearly a tornado. NWS said that, it looked like the outflow from a storm to the south was ingested in the parent cell, which increased the strength of the updraft and added aggregation of low level vorticity, which was already present because of synoptic front nearby.