The past few days, I've been optimistic about getting the entire Indy 500 in without rain. I'm feeling more and more confident about that happening with the latest data this morning. Most of the moisture that has been over the Midwest and Indiana the past few days will be shifting east, with drier air aloft moving in from the west tonight. With this dry air above the surface, it will be difficult for storms to develop tomorrow afternoon. There will be a cold front approaching the area, which will result in some isolated to scattered storms developing in Indiana, but I expect that they will hold off until after the race ends. I'd put the chance of getting the entire race done with no rain delays at 90%. The day will likely start off with some clouds, but these clouds should gradually decrease through the morning, leaving partly cloudy skies by the start of the race. Temperatures will reach the lower 80s, and winds will be between 8 and 12 mph, generally from the south-southwest.
Enjoy the race, it's going to be epic.