by Stephanie CrosbyKentucky Derby Festival officials announced this morning the theme for this year’s Thunder Over Louisville.Earlier this year, festival leaders announced the theme for the festival itself is “Spring Fever Reliever” and the Thunder theme plays off that medical reference. “Thunder Fever” is set this year for April 17th.UPS, Horseshoe Casino, E-ON U.S., and Meijer are the returning corporate sponsors for the free event. UPS spokesperson Mike Mangeot says even when companies are having to cut costs, Thunder is a good investment.“It makes everybody happy too," says Mangeot, "and win-wins like this are very important in these economically fragile times, when everyone’s sponsorship dollars are stretched so thin.”Kentucky Derby Festival President and CEO Mike Berry says while Thunder has been completely funded by its four returning corporate sponsors, the entire festival still has a little bit of fundraising to do.“Sponsorship in general has been as challenging as it was last year," says Berry. "The good news is, even with an entire month left to sell, we’re probably only five to seven percent from goal.”Producer Wayne Hettinger says the soundtrack for the show is already in the hands of the fireworks designers for the April 17th show. It’s the annual kickoff to the Kentucky Derby Festival.