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June-July 2007

Strong winds damage hangar roof at Jeffco

Microburst one possible explanation

wind damage

The roof materials landed about 200 yards (183 meters) north of the hangar. (Photos courtesy John Pereira.)

On Monday, June 11, exceptionally strong winds blew off a 5,000-square-foot section of the roof of NCAR’s aircraft hangar at Jeffco. The incident occurred at 3:26 p.m. and lasted only 20 seconds. The roof materials landed in the parking lot of Redstone College, about 200 yards (183 meters) north of the hangar. The wind also blew open several of the hangar’s doors, which weigh about 17,000 pounds, and blew two off their tracks.

Nobody was hurt, and no property in the area other than the roof was damaged. Security video cameras caught the incident on tape from several vantage points. The videos show strong south winds bending nearby trees, with a section of the roof flying off the hangar’s southeast corner just above a single open door.

“There was a big booming sound, and all the loose materials in the hangar started blowing around and the doors were moving without anyone touching them,” says Al Schanot (EOL), who was in the hangar at the time.

“I was running to try to close the door,” adds Brent Kidd, who was also in the hangar at the time, “but there was a loud boom and I looked up and a section of the roof was gone.”

jeffco damage

A 5,000-square-foot section of the hangar’s roof was blown off by strong winds

According to John Pereira, director of Physical Plant Services, the hangar roof is designed to International Building Code standards to withstand steady winds up to 100 miles per hour, and three-second gusts up to 120 mph. These are higher standards than the required construction codes for the area, he says.

A dry microburst is one likely explanation for the incident, as a weak storm cell passed near Jeffco at the time. “It was possibly a microburst, but closer examination of radar data would be required to be certain,” says Jim Wilson (RAL). “It’s really hard to determine without a series of radar images and precise mapping of locations and times.”

A dry microburst is a small, intense downdraft generated by precipitation falling into very dry air during which the rain nearly completely evaporates before reaching the ground. Microbursts can produce extremely strong winds that curl outward as the cold air of the microburst moves away from the point of impact with the ground. The wind gusts, which may approach 120 miles per hour, can be very dangerous for aircraft taking off or landing and are estimated to have caused up to 20 major airline crashes.

The possibility of a microburst damaging the hangar presents an ironic twist, since research on microbursts spearheaded by NCAR in the 1980s led to the development of radar-based microburst warning systems in place at airports around the country today. Since then, no further aircraft crashes have been attributed to this phenomenon in locations where microburst detection radars are in place.

 


In this issue...

Christmas in August

Nuts about science

NCAR welcomes new researchers

SOARS protégés in the thick of another summer

Just before Sunrise....

Strong winds damage hangar roof at Jeffco

Short Takes

Bill Randel to lead ESSL/ACD

Just One Look


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