The Storm Prediction Center just put out a Mesoscale Discussion for parts of southeast Missouri, southern Illinois, western Kentucky, and southwest Indiana. Basically, the MD lets the public know they are monitoring a specific area for a possible watch (severe thunderstorm or tornado).
A warm front is lifting northeast across the area. The concern is that the warm front will act as the mechanism to get thunderstorms to pop. I think the majority of thunderstorms will stay confined to near the front. There could be a few sporadic thunderstorms popping south of the warm front in the "warm sector".
We do have a pretty humid air mass in place. At noon (CT), temperatuers are in the middle to upper 70°'s and dew points are in the lower to middle 60°'s. That is plenty enough "juice" to get things going.
Here is a look at the instability in the atmosphere.
This thermodynamic field is called CAPE. CAPE stands for Convective Available Potential Energy. More specifically, this is SBCAPE (Surface Based Convective Available Potential Energy). This ultimately is the amount of instability in the atmosphere.