Friday continues to have a high chance of showers, with thunderstorms possible at times. An upper level disturbance will be moving over the area, and in a moist environment, there will be numerous showers throughout the day. Picking out a time for showers is tough, because they could happen at any time, but the early to middle afternoon hours appear to be the most likely period for rain. Around a quarter inch of rain is likely on Friday, with up to a half inch possible if a stronger storm crosses the Speedway.
Saturday looks better as the upper level disturbance will move away, and a weak high pressure ridge will build in. There will still be a lot of moisture in the atmosphere, so with afternoon heating, some scattered showers and storms could pop up. But I expect that the chance of one hitting the Speedway is low. The race is more likely to have dry conditions than wet conditions, but we'll have to keep an eye on the radar and see what develops.