Here is the forecast for the Iowa State Fair for Monday August 17th.

NWS: Mostly Cloudy with a 40% chance of Thunderstorms, 79° Light NW Wind.
WX Underground: Partly Sunny with a 50% Chance of thunderstorms, 77° Light NE Wind becoming NW.
WHO-TV: Partly Sunny with scattered showers, 80°
KCCI-TV: AM Showers 80°
ABC5: Partly Cloudy (Rain SE) 80°

Grade: B/B- (C if it rains) The forecast is all over the board for Monday. The later in the day however, the weather will get better.