Did "gustnado" topple Indiana stage? Experts divided

MIAMI Tue Aug 16, 2011 5:10pm EDT

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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)

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Comments (4)
candide08 wrote:
The stage was not constructed properly (obviously).
As soon as it “racked” gravity was working against it – and it collapsed.

If the base had been wider than the top (a bit pyramidal) the initial gust of wind would have had to fight against gravity and the infrastructure might not have collapsed.

Aug 16, 2011 7:45pm EDT  --  Report as abuse
pastormikeb68 wrote:
I am curious as to why this *new* term has not been commonly used before now? Did some meteorologist just make it up?

Aug 16, 2011 12:23am EDT  --  Report as abuse
myweatherlab wrote:
@pastormike68 the term gustnado has been around for many many years, it is one of those terms that you do not hear about that much due to the fact one has never caused any deaths.

Here is the Gustnado definition from the NWS.
A slang term for a short-lived, ground-based, shallow, vortex that develops on a gust front associated with either thunderstorms or showers. They may only extend to 30 to 300 feet above the ground with no apparent connection to the convective cloud above. They may be accompanied by rain, but usually are ‘wispy’, or only visible as a debris cloud or dust whirl at or near the ground. Wind speeds can reach 60 to 80 mph, resulting in significant damage, similar to that of a F0 or F1 tornado. However, gustnadoes are not considered to be a tornado, and some cases, it may be difficult to distinguish a gustnado from a tornado. Gustnadoes are not associated with storm-scale rotation (i.e. mesocyclones) that is involved with true tornadoes; they are more likely to be associated visually with a shelf cloud that is found on the forward side of a thunderstorm.

Aug 17, 2011 6:42am EDT  --  Report as abuse
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