Severe Weather Targets the Mississippi Valley Today

There is a risk of severe weather this afternoon for states around the Mississippi Valley. This comes as a frontal boundary sags southward and a dry line is located out west.

This is a sounding valid for 18z tonight, known as 7 pm Central time. When you get the dashed line to the right of the soldi blue line, that is when you develop instability. As you can see, there is a large gap between the solid line and dashed line, indicating a lot of instability. CAPE shown on the sounding indicates over 3000 j/kg of instability present at that time.
Another thing seen on the sounding is something called 'ConvT', which appears to indicate the temperature when air will rise to produce thunderstorms. To figure out the surface temperature, I use 28 degrees Celsius, as the solid temperature line is in that 25-30 Celsius area closest to the bottom of the image. Converting 28 Celsius to Fahrenheit results in a temperature of 82.4 degrees F, a good 2 degrees above the ConvT of 80.4 F.
A couple final indices: The Hail index shows hail of 1.5 inches is possible. The hail index is the first parameter in the 4th column labeled 'Hail'. The Supercell Potential parameter, 3rd result in the 2nd column, indicates a 60% chance of a supercell if convection were to develop (which it will).

I don't blame you at all if you don't understand this- I just started getting the gist of it recently after a lot of researching and learning, so my apologies if I am confusing you.
In short, thunderstorms, with a fair chance of becoming supercells, are possible today.

-Andrew