Hail and Damaging Wind in Ohio, April 10, 1999

Synoptic and mesoscale conditions on April 10th, 1999...A strong low pressure system was located near St. Louis, MO during the afternoon of April 10, 1999 and was forecast to move northeast into southern Michigan by 12z on the 11th. Although the boundary layer was quite stable across northern Indiana with surface temperatures in the middle 50s and dewpoints in the low 30s... very unstable air was located south of the warm front draped through the Ohio valley. As low pressure intensified during the afternoon of the 10th...a strong low level jet (60 knots) developed from southern Illinois into central Indiana. Most unstable parcel CAPE lifted from 800 millibars were on the order of 1500 J/kg... lifted indicies from -3 to -5...and amazing storm relative helicity values near 1000 m2/s2. Strong mid-level convergence in association with the upper low in Missouri and attendant 80 knot jet combined with strong low-level theta-e advection over the warm front and increasing large scale ascent ahead of the 250 millibar 130 knot jet max triggered a line of severe thunderstorms over northeast Illinois by late afternoon. This line of storms continued to intensify as they raced eastward at 40 knots. With low freezing levels in place and cooling aloft as the upper low pushed northeast...widespread severe hail fell in nearly every county across northern Indiana that evening. Two elevated supercells developed ahead of the main line in northwest Indiana early that evening and marched eastward. The first supercell tracked from Lake county east into Lagrange county before weakening. The second supercell developed further south across Jasper county and moved east into Allen county before weakening. Both were very efficient hail producers with some locations reporting several inches of hail accumulation on the ground. Additionally both produced several funnel clouds which stayed aloft likely due to the elevated nature of the convection and very stable boundary layer which prevented most of the rear flank downdraft from reaching the surface.