Abstract
Four tornadoes, of F1–F2 intensity, occurred over Barron County, Wisconsin, on the evening of 11 September 1990. The tornadoes were associated with a slow-moving thunderstorm cluster that developed along a warm front, and all occurred within 17 km of Rice Lake over a 2-hour and 15-minute period. National Weather Service radar data indicate that the tornadoes probably were associated with mesocyclones. Hail up to 7 cm in diameter and damaging winds also were reported over Barron County and three adjoining counties. Forecasting of slow-moving thunderstorms within an environment capable of producing mesocyclones and tornadoes remains an important forecast problem. Analysis of features that produced quasi-stationary thunderstorms and a vertical wind profile sufficient to generate mesocyclones hopefully will improve recognition and forecasting of similar events in the future.
