Here is the Forecast for the Iowa State Fair for Wednesday August 19th.

NWS: Mostly Cloudy with Thunderstorms likely in the AM, 80° SSE Wind 8-13mph.
WX Underground: Mostly Cloudy With Thunderstorms in the morning, then again in the afternoon. 79° South Wind 10-15mph.
WHO-TV: Thunderstorms likely 79°
KCCI-TV: Mostly Cloudy with Thunderstorms Mainly before 1pm 80°
ABC5: Scattered Thunderstorms 78°