Here is a the Significant Tornado Index (STI) in red superimposed over population. Chicago toward upper left and Atlanta lower right. With values of 2 or higher conducive to major, long-track tornadoes.
If a thunderstorm approaches with a value of 2 or more you are in extreme danger! These storms are moving very fast, so you need to be proactive about gathering information today.
Each of these large storms, crossing these high STI values, means that tornadoes will likely develop and sustain themselves as they move east at 50-55 mph.
New storms are developing near the Alabama-Tennessee border region. Keep an eye out there, as well.