Take it from someone that lives in MISSISSIPPI that you really do not want to visit during the months of late May, June, July, August and most of September. I'm in west central MS and it doesn't cool off until Halloween here. Now it is cooler in October but we still have to run a/c! Around Thanksgiving it get dreary some days and Jan - Feb tends to be the coldest time and if it is going to sleet or ice it will be in February.
March, April and early May or late September through Thanksgiving is when I would travel the lower states.