Thunderstorms are started to "pop" in the afternoon heat. It first started with a storm along the Kentucky/Tennessee border. As the thunderstorm got larger, a gush of cold air came rushing out of it on the north side. The cold air coming out of it is acting a small cold front.
As the leading edge of colder air moves away from the storm in an outward moving circular shape, similar to a pebble dropped in to a pond, it will help lift moisture at the surface and create thunderstorms. As the line bumps in to already developed thunderstorms, there is a chance some of the storms will quickly intensify.
The storms will be slow movers. The biggest threat from the storms will be damaging wind, large hail, and heavy rain.
Here is a three dimensional view of the storm that is moving through northwest Tennessee. It has already had a history of producing golfball size hail and damaging winds.
The top of the storm has climbed to over 45,000 feet. Most likely, if you go outside and look to the south, you will be able to see it from a pretty good distance.
Speaking of heat... Yesterday's 89° official high temperature at the Cape Girardeau Regional Airport was the warmest day in 269 days. The last time we had been that warm was August 27, 2009.