F2 tornado in De Kalb County, Indiana

On Wednesday 10/24/01 a surface low pressure system tracked rapidly northeast from the mid Mississippi Valley to northern Lake Michigan and deepened significantly. The accompanying cold front surged east from the Mississippi Valley during the afternoon to southeast Michigan and western Ohio in the evening. The deepening surface low was the result of a negatively tilted upper level trough approaching the Mississippi Valley. The air mass ahead of the cold front was quite unstable with lifted indices around -5C and surface dewpoints of 65-70F. Strong veering wind fields were over the area with 20-30kt S-SSE flow at the surface veering rapidly in the low levels to southwest at 45kts, then remaining unidirectional above with wind speeds increasing to 65kt at 20,000 ft. An area of Thunderstorms across Illinois in the early afternoon formed into a line as they moved into northwest Indiana. Two strong bow echoes developed over northwest and north central Indiana during the late afternoon and moved northeast at 50 MPH into southern Michigan. Numerous tornadoes occurred in the comma heads of the bow echoes. Isolated supercells ahead of the main squall line produced little severe weather except for a tornado that occurred over northwest Ohio in the evening when the squall line merged with a supercell.