Midwest Overview - September 18-24, 2002

The week of September 18-24 was quite wet and at times stormy in the Midwest. A tornado outbreak occurred on the 20th, with at least 3 significant tornadoes (two F2 and one F3) afflicting Indiana, and some weaker tornadoes elsewhere in Indiana and in Ohio. These storms occurred ahead of a strong cold front that brought lots of rain as it slowly traversed the Midwest. Since there was also significant rain at the beginning of the period, the total amounts for the week were 1.5 to 3.5 inches in a band from southeastern Missouri to southeastern Michigan, and over an inch elsewhere in most of the Midwest (Figure 1). Significant rain also fell in a clipper system crossing northern Michigan on the 24th. The band mentioned, surrounding zones, and northern Michigan all received more than 200% of normal precipitation for the week (Figure 2). Only eastern Ohio and southern Minnesota missed out on the rain, and were considerably drier than normal. Temperatures for the week ranged from near normal in the western Midwest to more than 7°F above normal in the eastern Midwest, with a smooth west to east transition (Figure 3). Due to the rain, some drought relief occurred in southern Illinois and southwestern Indiana, where severe drought (D2) improved to moderate drought (D1) status (Figure 4), National Drought Mitigation Center). Drought remained strongly entrenched in the eastern Ohio Valley, and dryness increased in the northwestern quadrant of Missouri.

The occurrence of tornadoes in September is not all that unusual in the Midwest. However, the outbreak on September 20th was unusual in its intensity for the time of year. A total of 27 separate tornado reports were submitted to the Storm Prediction Center (SPC), 24 from Indiana and 3 from Ohio (Figure 5, SPC). Analysis by the Indianapolis National Weather Service (NWS) Office revealed that most of the reports in Indiana were associated with one supercell that spawned at least 3 separate tornadoes, two with F2 damage and one with F3 damage. The damage path of the F3 tornado was 112 miles in length, although the intensity was less than F3 over most of its course (Figure 6, Indianapolis NWS). The frontal boundary was translating from west to east, but the individual cells, including the large supercell associated with the F3 tornado, were moving to the north-northeast along the front. Figure 7a, Figure 7b, and Figure 7c show a sequence of NWS radar images tracking the front from the start of the F3 tornado life to near its conclusion.

Damage assessments in Marion County alone (the location of Indianapolis) reached more than $36 M, with more than 313 buildings damaged or destroyed. There were 97 injuries in Marion County, and many more along the path, but due to warning times exceeding 15 minutes in most cases, there were no deaths. About 80,000 customers lost power in the Indianapolis area after some high voltage feeder lines were snapped when their transmission towers hit the ground. The towns of Martinsville and Greensville were the worst damaged in that area, housing the majority of the completely destroyed homes in the outbreak. One of the F2 tornadoes in far southwestern Indiana smashed Posey County, destroying at least 15 trailer homes. The 32 counties affected by the tornadoes and other storms along the front in Indiana have received a Federal Disaster Declaration (Figure 8, Federal Emergency Management Agency). In Crestline, Ohio, a light tower at a fair was blown over, injuring 10 people, including one critically. However, the tornadoes in Ohio were brief and much weaker than those in Indiana. Interestingly, some Indiana health department experts on vector borne illness stated that the heavy rains and winds may reduce the success of mosquito breeding at the end of the season, possibly curtailing the spread of West Nile virus this year.