Outflow Boundary Vs. Indiana Fairgrounds Stage Collapse

Aug 13, 2011; 10:17 PM ET

A stage collapsed at the Indiana Fairgrounds in Indianapolis tonight around 8:55 PM. The National Weather Service estimated winds at 60-70 mph.

When I first looked at the radar I was surprised that a line of storms hadn’t hit the site (north of town). However, looking closely at the radar loop it was clear that an outflow boundary preceded the storm.

Outflow boundaries can be out in front of thunderstorms by several miles. This could have made people think they had more preparation time than they did, because it preceded the rain and lightning by 10 or 15 minutes.

You can download a radar loop here (reflectivity or velocity winds). The only weather station in the area was south of town and recorded a sudden 41 mph gust.