Storm Reflectivity and Mesocyclone Evolution Associated with the 15 April 1994 Squall Line over Kentucky and Southern Indiana

Abstract

A long-lived highly organized squall line moved rapidly across the middle Mississippi and Ohio Valleys on 15 April 1994 within a moderately unstable, strongly sheared environment. Over Kentucky and southern Indiana, the line contained several bowing segments (bow echoes) that resulted in widespread wind damage, numerous shear vortices/rotational circulations, and several tornadoes that produced F0–F2 damage. In this study, the Louisville–Fort Knox WSR-88D is used to present a thorough discussion of a particularly long-tracked bowing line segment over central Kentucky that exhibited a very complex and detailed evolution, more so than any other segment throughout the life span of the squall line. Specifically, this segment produced abundant straight-line wind damage; cyclic, multiple core cyclonic circulations, some of which met mesocyclone criteria; several tornadoes; and embedded high precipitation supercell-like structure that evolved into a rotating comma head–comma tail pattern. The bowing segment also is examined for the presence of bookend vortices aloft and midaltitude radial convergence. In addition, the structure of other bowing segments and their attendant circulations within the squall line are discussed and compared with existing documentation. Radar sampling issues and ramifications of the squall line’s complicated structure on the warning process of future similar severe weather events are touched upon as well.