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MIAMI (Reuters) - Was the sudden wind gust that collapsed an outdoor concert stage in Indiana at the weekend, killing five people, a 'gustnado,' a sometimes powerful whirlwind that scoots ahead of thunderstorm fronts?
Senior meteorologist Henry Margusity of private weather forecaster AccuWeather.com believes that it was.
He cites video footage of the event at the Indiana State Fair which he says shows the characteristic rotating swirl of a gustnado whipping around dust and even a large flag, before the stage collapsed to the screams of terrified spectators.
Five people were killed and scores more injured in the accident, which occurred late on Saturday just minutes before the country duo Sugarland was set to begin performing.
"If you analyze the video, you can see that gustnado kind of coming across and moving through and everything's twirling around as it goes through," Margusity told Reuters.
He believed the gustnado could have boosted already strong winds blowing to gusts of possibly up to 60 miles per hour (100 km per hour) or more.
The U.S. National Weather Service defines a gustnado (or gustinado) as "a small whirlwind which forms as an eddy in thunderstorm outflows." It distinguishes them from tornadoes, those powerful, destructive and often deadly funnels of wind common in the U.S. Midwest.
But Harold Brooks, research meteorologist at U.S. government weather agency NOAA's National Severe Storms Laboratory, disagreed with Margusity's analysis, saying he saw no evidence that a gustnado was involved in Indiana.
He believed the winds that struck the concert stage at the Indiana State Fair were "straight line winds."
"It's not clear that the winds were very strong," he told Reuters, adding winds of 40-50 miles per hour (64-80 km per hour) associated with thunderstorms were not uncommon.
Margusity said a 'storm chaser' in the area was filming several gustnados associated with a thunderstorm front just south of the stadium around the same time as the accident.
Both experts did agree however that gustnados, which are similar to the so called 'dust devils' that often whip across the U.S. central and western plains, rarely kill anyone.
"I've never heard of fatalities due to a gustnado ... It happened to hit the wrong spot at the wrong time," Margusity said.
"If conditions come together ... it doesn't take much for a meteorological event to become a major societal event," said Brooks, commenting on the deaths.
State fire marshals and the Indiana Occupational Safety and Health Administration are investigating the collapse.
Editing by Jerry Norton