This does not look like the 2015 race that had to be stopped due to heavy rain. I can see the final 3-4 hours of the race being affected by some on/off light to moderate rain showers. The main impact may be on the campers Saturday night as the rain gets heavier. Rain amounts overnight are expected to be in the quarter to half inch range, with additional rain on Sunday. If you're camping at the track, be prepared with some wet weather gear.
I'll have another forecast update on Friday at the latest, and earlier if there are significant changes to this thinking.