A Localized severe weather event over southwest Ohio on 24 August 1996

During the early morning hours of August 24, 1996, two separate sub-severe convective systems converged over southwest Ohio. This merger resulted in rapid intensification, with associated bow echo development and localized severe weather soon to follow. Through in-depth analysis of the KILN WSR-88D radar data, a Mid-Altitude Radial Convergence (MARC) signature of 50 kts, which has been shown to be a reliable predictor for damaging surface winds, was observed. Marginal severe damage did indeed occur in association with this signature. However, the most significant wind damage from this convective system occurred in conjunction with an attended cyclonically rotating Book End Vortex (BEV), a signature which often follows the MARC signature.

This paper will examine, not only the storm scale aspect surrounding this event, but also synoptic and mesoscale features that most influenced the occurrence of this localized severe weather incident. It will be shown how this storm merger occurred in a moderately unstable environment, with marginally noted surface-based forcing, and was strongly influenced by the juxtaposition of an upper level jet. Further analysis will show how the existence of a well defined transverse ageostrophic secondary circulation, in connection with the right-rear entrance region of this upper level jet, acted to enhance the upward vertical motion through a deep atmospheric layer over southwest Ohio. Also of prime importance was that this storm developed in an environment conducive to microburst activity, where qe differences of 25° K were noted between the surface and mid-levels.