Anyone know what week the festival for the Kentucky Derby starts?

Every year, the Kentucky Derby starts off with an explosion about two weeks before the race. Thunder over Louisville is a sight you absolutely cannot miss, this year it takes place on April 18, 2009. Thunder as we lovingly call it brings in people from all over the country with the world's biggest fireworks show. The crowd has been in past years as big as 800,000 people. The day starts early with people lining the riverfront in search of a good seat for the airshow, the Chow wagon, and the general spectacle that is Thunder over Louisville