Friday will be a nice day with plenty of sunshine and pleasant temperatures near 70. It will be quite breezy, with a northwest wind between 15 and 25 mph, with gusts around 30 mph at times.
Rain is expected to arrive at Road America around noon on Saturday, and persist for several hours. There is a small chance that there could be a few thunderstorms as well, but the main impact will be the rain showers. Total rain amounts on Saturday afternoon will likely be around a quarter of an inch, possibly up to a half inch. I expect with this amount of rain, there could be some delays to some of the sessions.
Sunday's weather looks much better behind the departing low pressure system, with mostly sunny skies and highs in the lower 70s.