On Wednesday night, an upper level trough and a cold front will move across Indiana. Most of the showers and storms with this front will occur overnight, and should be cleared out from the track Thursday morning. But the front will linger across southern Indiana through the afternoon, which will keep a low chance of showers in the area as the MRTI series begin their practice sessions late in the day. It will be a breezy day as the front moves through, with winds shifting from the southwest in the morning to the northwest in the afternoon.
The front begins to push back to the north on Friday, moving across central Indiana around the middle of the day. This will increase the chance of showers as a surge of moisture spreads northward with the front. Friday appears to have the greatest potential to be affected by rain. While rain amounts are too uncertain to project this far out, it does not appear to be a heavy rain pattern that would cause cancellations, but the threat of a shower will persist all day.
The front will continue to push north, and will be located near the Indiana-Michigan border Friday night. A low pressure system will track east along the front Friday night and Saturday. Most of the shower activity will likely be located north of the Speedway on Saturday, but there may be enough instability to allow some scattered showers to develop in the afternoon. If the models change and the front ends up stalling farther south than currently expected, then the rain chances for Saturday will rise.
The details on the timing and amounts of rain at Indy will become more clear over the next few days. Hopefully we'll be able to update the forecast in a drier direction over the next few days.