Central Illinois Cold Air Funnel Outbreak

Abstract

Numerous cold air funnels developed in close proximity over central Illinois on 23 May 1988 as the core of an upper-level cutoff low pressure center passed over the region. Five separate funnels were observed by one of the authors from a single location over a period of 33 min. Images of these funnels captured from video are presented, one showing two funnels extending toward one another from the same cloud and two others illustrating stages in the life cycle of one of the funnels. Surface and upper air analyses, radar data, and two soundings taken at the time of the outbreak are presented to illustrate the environment in which these funnels formed. The family of cold air funnels occurred along a weak stationary front. The fact that so many funnels occurred along the same line is suggestive of a vortex sheet breaking down due to the development of horizontal shearing instability. If this is the case, then the cold air funnels observed on 23 May are similar dynamically to nonsupercell tornado families that develop along cold fronts and outflows.