EF2 tornado in Knox County, Indiana

At 1456EST, this EF-2 tornado touched down 4.5 miles west-northwest of Decker. The most extensive damage was found north of Decker along Old Decker Road, just to the east of Route 41. The second story of a home was removed with the exterior walls collapsed. This tornado continued until it was 6 miles southeast of Vincennes at 1506EST. The estimated maximum wind speed with this EF-2 tornado was 130 mph.

A large outbreak of severe weather took place on November 17, 2013. In Indiana alone there were 29 tornadoes, with dozens more in other states. In central Indiana the strongest tornado was rated an EF-3. There were 8 EF-2 tornadoes, 6 EF-1 tornadoes, and 1 EF-0 tornado in central Indiana. This number of tornadoes for the entire state is the largest outbreak for November in recorded history for Indiana, and the third largest outbreak in state history for any month (June 2, 1990 is first with 37 tornadoes, April 19, 2011 is second with 29 tornadoes).

A potent weather system moved into the Ohio Valley during the afternoon of November 17, 2013. The setup became ideal for severe weather, including multiple tornadoes. A strong jet stream was approaching central Indiana during the afternoon of November 17. An upper trough was approaching the area as well. Not far off the surface, strong winds were flowing north from the Gulf of Mexico. Speeds at 500 meters over Indiana at 3:00 PM were over 50 mph. This system's setup provided the area with plenty of instability for thunderstorms to form. The turning of the winds with height, set up by the approaching upper trough and winds ahead of the surface cold front, set the stage for the potential for tornadoes. The effective storm relative helicity values, by mid-afternoon,were 500 to 700 m2/s2 across central Indiana and were extremely high for November. As a result of this setup, numerous thunderstorms developed across Illinois and quickly became severe. These storms produced numerous tornadoes across Illinois. The strong winds aloft caused the storms to move quickly into Indiana, where additional tornadoes and severe thunderstorms developed.