8/04 Storm video
http://www.weather.com/weather/videos/news-41/top-stories-169/closing-act-storm-halts-lollapalooza-29969
Storm shown from the lake shore 150,000 people lost power. 75,000 of which were in Cook County alone.

8/04 Lollapalooza reopens after heavy storm puts on show
http://www.chicagotribune.com/news/local/breaking/chi-chicago-weather-forecast-saturday,0,2262040.story
The incoming storm front hit about an hour into the evacuation,  and mostly calm crowds on Michigan Avenue gave way to yelling clumps of people sprinting towards the nearest shelter as a greenish-gray dark clouds devoured the sky and torrential rain began to fall.