On Friday there will be an upper level trough of low pressure moving west to east across Tennessee. This will mainly increase cloud cover over Nashville, although I can't completely rule out a shower late in the day or evening. I don't expect that it will have much of any impact on the racing, which ends before 7 pm. There is a concert from 7 pm to 9:30 pm that could be a brief shower or sprinkle. But the chance of this appears low.
On Saturday the trough will exit and high pressure will build in. This will bring mostly sunny skies and warmer temperatures near 90. Sunday looks much the same, but a little warmer, with highs in the lower 90s.