Hail in Posey County, Indiana

Penny size hail was measured in far southern Posey County, associated with a supercell which produced a tornado in Union County, Kentucky.

A 500mb shortwave trough moved across the Upper Midwest with height falls across the Quad State during the afternoon and evening of the 16th. The exit region of a strong (125kt) upper level jet was positioned across the area as well. Low-level winds strengthened during the afternoon to 50kts at 850mb. Following the early AM convection, ample sunshine allowed for a very unstable airmass to develop with CAPE of 3000-4000J/kg with deep layer shear of 65-70kts. Late afternoon, STP peaked at 9 near the Wabash/Ohio River confluence with effective SRH of 300-400m2/s2. Mid-level lapse rates peaked at 8-8.5C/km for much of the Quad State (though lower for Southwest Indiana) with significant hail parameter of 3-5 mid-afternoon and DCAPE peaking at 1200-1500J/kg. Initial storm formation was discrete with very large hail and tornadoes, with storms becoming more linear later in the evening.

Despite the very strong setup, Southwest Indiana was fortunate to find a gap between the mid-afternoon storms that went through St. Louis and tracked east-northeastward, and the evening storms that crossed just to the south, resulting in a lone sub-severe hail report for Southwest Indiana.