Chattanooga is a neat little town. Very historical with a lot of Civil War history. I am a history buff on that stuff and we took our kids to one of the battlefields.
Chattanooga is one hell of an industrial city as well. In 1969 it was the most polluted city in the US with smog worse than LA being in a bowl like shape surrounded by mountains. I-75 at the GA line has been noted for some huge wrecks by fog...
I went in May, 2010. Was almost 90 degrees but felt great at Rock City, like 15 degrees cooler...We had some thunderstorms the whole trip...