Outflow Boundary Vs. Indiana Fairgrounds Stage Collapse
UPDATE: AccuWeather.com Meteorologist Henry Margusity believes it could have been a gustnado (a small swirl occurring on gust fronts) which downed the stage. Given the lack of damage elsewhere on the fairgrounds, and noting a possible swirl of dust in the video below, I think it's plausible. However, swirls in the wind are omnipresent, caused by objects on the ground and friction with the earth; we just need dust, snow, etc. to see them.
UPDATE: The fairgrounds is now closed and we have a story up with more details about the event. The best YouTube video of the event is embedded below. Make sure to read AccuWeather's Mike Smith's words on how action could have taken place earlier. Tom Skilling also reminds us that lightning is a danger at these events. Is it time to take action that will keep people safer?
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 (also known as gust fronts) 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.
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