Hail and Damaging Winds in Ohio, June 19, 1998

Synoptic and mesoscale conditions for June 18/19, 1998...A large upper level ridge was in place across the central plains states the morning of the 18th with an upper level trough axis anchored across the eastern Great Lakes region. An unseasonably strong shortwave trough was forecast to crest the upper ridge axis and dive southeast across the midwest during the afternoon and night of the 18th. At the sfc, a warm front was lifting northward with low pressure developing across eastern South Dakota. This surface low was forecast to track into central Wisconsin by evening as a 60 knot low level jet developed in response to a coupled 250 mb jet streak structure. A mid level capping inversion inhibited convection during the day but with the approach of the mid level trough and cold pool, steep mid level lapse rates developed with 700 to 500 mb delta T of 20 degrees Celsius. Rich boundary layer moisture began to pool along the warm front in the afternoon with surface dewpoints climbing into the lower 80s across central and eastern Iowa where severe convection first intiated. Dry air punching in behind this system and favorable storm relative shear provided a balanced cool pool/ambient shear interaction which maintained this long lived severe convective system.A large squall line know as a derecheo developed across central Iowa during the afternoon of the 18th and rapidly propagated eastward along and south of the warm front. Wind damage... large hail and very heavy rains were common from Iowa east into Ohio were the squall line weakened during the morning hours of the 19th. Damage across Indiana, Michigan and Ohio was primarily due to strong straight line winds from 60 to 80 mph which downed many trees and power lines.