WeatherWhys for July 11,2014 from accuweather.com

Thunderstorms can be regarded as nature's air conditioners. On a typical summer day, temperatures will rise steadily through the early afternoon as clouds will build into thunderstorms. Once that thunderstorm passes over a given location in the late afternoon, temperatures will come crashing down as much as 15 to 20 degrees as the thunderstorm pulls down much cooler air from above the surface.