Midwest Overview - December 15-21, 2002

The period of December 15-21 was wet for the time of year, with rain exceeding 2-3 inches in places in the south central Midwest (Figure 1). Most of the region received more than 0.5 inches of precipitation, with amounts exceeding 200% of normal over a broad portion of the central Midwest (Figure 1a). Despite the available moisture, snow fall was minimal over most of the region (Figure 2), as temperature were very warm during the period. All of the Midwest was above normal in temperature, with the western 70% more than 10°F above normal (Figure 3). The Drought Monitor map for the week reflected conditions before the major precipitation event on the 17th and 18th, showing that drought intensification had been continuing prior to the storm (Figure 4, National Drought Mitigation Center).

The storm that entered the southwestern Midwest on December 17 was unusually strong and convective for the time of year. A deep layer of southerly moist air flooded the region ahead of the cold front, with dew points in the 50s commonplace (Figure 5, U of Illinois Dept. of Atmos. Sci.). In addition, a strong southwesterly jet was in place overhead, providing rotation through the atmospheric column. Supercell thunderstorms with rotation started forming about 8 PM local time in southwest Missouri, and at least 20 distinct supercells were identified by the Springfield, MO, NWS office over the next 18 hours. Five separate tornadoes developed (Figure 6, NWS), with a total of 10 sightings reported. Two people in Missouri were killed, one in an F2 tornado that struck the Lucky Lady Mobile Home Court near Chesapeake, MO, and another in an F1 tornado that destroyed three houses in Barton County, MO. There was a total of at least 16 serious injuries in the combined casualty count for these two events, and a number more at the other storms spread around the state. The strongly tornadic conditions shifted to the south of the Midwest late on the 18th, bringing more death and destruction. Heavy rain did continue in the Midwest (Figure 7, UIUC DAS) as the elongated cold front slowly moved across the region and the low pressure center mover north of the Great Lakes.