EF1 tornado in Henry County, Illinois

Brief tornado touchdown southwest of Atkinson, IL. Rated EF1 with peak winds at 100 mph, a path length of 0.3 miles, and a path width 30 yards. The roof of a large outbuilding was significantly damaged and the debris was scattered over a quarter mile to the northeast.

A strong and quick moving cold front made its way through the Midwest. The environment ahead of the cold front was unseasonably warm, with temperatures in the upper 60s and readings in the 40s not far behind the front. This led to strong baroclinicity along the front, and subsequent convection with just the right amount of instability. This is considered a high shear low CAPE (HSLC) event, where organized severe thunderstorms are favored in this environment. Potential hazards are damaging winds, large hail, and tornadoes. Six tornadoes were confirmed and several wind reports were received (ranging between 50-60 mph, with a few gusts over 60 mph). Damage reports ranged from structural damage to tree damage. Many residents were left without power in parts of northwestern IL, leading to some schools canceling classes on the 11th. Besides the strong winds, a few severe hail reports were received.

In addition, heavy rain occurred with some of the stronger storms, with rainfall totals over an inch. For how dry it has been, flash flooding was not much of a concern. While the environment was very moist and favorable for heavy rainfall, the fast storm motions led to little accumulation through much of our forecast area.