Thunderstorm Wind in Massac County, Illinois

A tree was blown down onto a house in Brookport.

A significant severe weather episode unfolded across southern Illinois around midnight on the 15th, as numerous severe storms produced tornadoes, damaging winds, and large hail. A strong negative-tilt 500mb trough moved northeast from Kansas to the Upper Midwest through the day and into the evening on the 14th. The associated 978mb surface low followed a similar track, and led to a rapid increase in low-level moisture just ahead of a trailing dry line that moved eastward across southern Illinois in the early morning hours of the 15th. The moisture return was sufficient for 1000-2000J/kg of CAPE to develop. Wind fields were extremely strong, with storm relative helicity in the 0-1km layer of 300m2/s2 and above, and 600m2/s2 in the 0-3km layer. The significant tornado parameter was over 6 which supported strong and long-track tornadoes. In addition, steep mid-level lapse rates around 8C/km supported very large hail. Two EF-2 tornadoes each produced a 15 mile path of destruction. One formed in far northern Jackson County and lifted northeast passing just west of DuQuoin and eventually struck the St Johns community just north of DuQuoin. The second tornado formed west of Vienna and moved northeast crossing Interstate 57 just north of Exit 14. It struck Bloomfield and then tracked through the Shawnee National Forest and lifted just before reaching Pope County. The tornadoes damage trees and power lines and did mainly roof damage to numerous homes, barns, and outbuildings. In addition to the tornadoes, straight line winds knocked down trees and power poles near Ava and Cutler, and knocked a tree into a house in Brookport. Hail up to the size of golf balls fell in Harrisburg.