Friday looks really nice as well as cars hit the track, with slightly cooler temperatures building in as winds shift to the north.
I expect that all the racing on Saturday will stay dry. However, a low pressure system is going to be tracking toward the area from the southwest. The most likely scenario is that the rain holds off until after the IndyCar race ends around 6 pm. I am mentioning just a slight chance of showers late in the day to account for the possibility that the rain arrives a little earlier than expected. After sunset Saturday evening, the rain chances will be rising, and I'd put the chance of rain Saturday night at 50%.
Although the surface low pressure area will move east of Detroit Saturday night, an upper level trough will remain over the area through Sunday. This unsettled pattern could result in some showers and thunderstorms threatening Sunday's events. While the showers will be possible at any time on Sunday, the afternoon will have the better chances of seeing a thunderstorm. There is still some uncertainty about the details of how Sunday's weather could play out, so stay tuned for updates as we get closer.