The prevailing weather pattern across Iowa will be a northwest flow through the weekend. This will provide mainly dry and comfortable temperatures and humidity. However, the models are indicating that a disturbance in this northwest flow will move across Iowa late Saturday into Saturday night. It may bring isolated to scattered thunderstorms to the area late in the afternoon and evening. While the timing won't affect the race, the Kenny Chesney concert that starts at 4:30 pm could potentially be affected, depending on the timing of storms. I don't know how long the concert will be, but right now, the most likely time period for storms is 6 pm to midnight. If that timing shifts a little earlier, then it could potentially affect the concert.