 The high humidity levels with dew points in the 70s°F (low 20s°C), temperatures that in many areas were near 80 °F (27 °C), strong wind shear, and the presence of the dry line helped develop the instability to produce severe thunderstorms across both the Midwest and the Southern Plains on October 17.A moderate risk for severe weather was issued by the Storm Prediction Center two days prior to the event.The storm then moved across the most of the Midwest on October 18, where a moderate risk was in effect also for two days for most of Illinois, Indiana, and parts of Kentucky; however, the moderate risk was revised further to the south and the east to include western Ohio, western Tennessee, southeastern Missouri, northeastern Arkansas, and a larger portion of Kentucky.