Tornadoes are always menacing. But a pair of them, side-by-side, is as horrifying as it is unusual. Double the terror, double the noise — and, sometimes, double the destruction.

Officials didn’t know for sure how much destruction there was Monday night after the twin twisters, separated by a mile at one point, ripped through Nebraska.

They weren’t certain which twister finally went where — or which one all but destroyed the town of Pilger, 60 miles southwest of Sioux City, Iowa.

It wrecked much of the town, claiming at least one life — that of a 5-year-old — and injuring at least 19 others, according to the Associated Press.

“More than half of the town is gone — absolutely gone,” Stanton County Commissioner Jerry Weatherholt told the AP. “The co-op is gone, the grain bins are gone, and it looks like almost every house in town has some damage. It’s a complete mess.”

Those who saw it said it was chilling.

“It was terribly wide,” Marianne Pesotta told KETV. “I had to get out of there. I drove east. I could see how bad it was.”

Those who survived it said it was terrifying.

“Our ears started popping … and we heard a swishing sound,” Ryan Kruger told the Omaha World-Herald. He and five of his co-workers hunkered down in a vault at the Farmer’s Cooperative. “About the time we figured it was over, the roof caved in.”

Darin Schneider told the newspaper he took shelter near a bridge at the lake, wrapping his body around a steel beam.

“It picked up my lower torso when it came through. But I gripped my legs back to the beam and got my bearings,” he said. “I was scared as hell. But if I wasn’t near the bridge, and I tried to make a mad dash for safety, I wouldn’t have made it.”

Emergency management operations officer Earl Imler told CNN late Monday that Nebraska is still in response mode, collecting damage reports from local officials. But they won’t know the intensity of the storms until late Tuesday at the earliest, after crews have examined the area, Barbara Mayes, a meteorologist with the National Weather Service, told the AP.

Mayes said the twin tornadoes were unusual because both appeared to have similar strength. In most cases, she said, one tends to be larger and more powerful than the other.

“It’s less common for two tornadoes to track together for so long, especially with that same intensity,” she said. “By no means is it unprecedented. But we don’t see it often.”

Tornadoes form from a supercell thunderstorm, which contains a large column of rotating air. It’s not uncommon for one twister to dissipate before another forms out of the same supercell.

But it’s much less common for the primary twister to keep going when the new one forms, producing the two simultaneously, said Greg Carbin, warning coordination meteorologist at the National Oceanic and Atmospheric Administration’s Storm Prediction Center.

“Nothing says there needs to be a gap” between two tornado touchdowns, he told The Washington Post. “There usually is. [Monday] there wasn’t.”

Carbin said smaller tornadoes also can form on the perimeter of a larger vortex — the spinning air. In fact, some of the most violent tornadoes often have more than one vortex. These twisters are called satellite tornadoes because they orbit the larger one.

These peripheral vortices may also be part of a larger multiple-vortex tornado – one that contains multiple vortices rotating around, inside and as part of the main vortex. Carbin said one of the more memorable double tornado days in the recent past was on May 3, 1999 — the day a total of 74 tornadoes touched down across Oklahoma and Kansas in less than a day.

Karen Kosiba, a meteorologist at the Center for Severe Weather Research, said that when both tornadoes are on the ground at the same time, they commonly create quasi-parallel paths of destruction — with one track running to the side of the other. But, she said, twin twisters don’t last long, since one of the tornadoes is in a decaying parent rotation — or dying faster.

Carbin added that, obviously, the more ground covered by the tornado, the greater the chance of substantial damage — though experts couldn’t confirm Monday night the character of Nebraska’s duo.

Still, Kosiba said, people are definitely intrigued by it.

“It’s not uncommon to see one or two or three, but this is two substantial-looking vortices,” she told The Post. “It looked like two substantial tornadoes were on the ground at the same time.”

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Reference: http://www.washingtonpost.com/news/morning-mix/wp/2014/06/17/the-double-tornado-that-slammed-nebraska-last-night-was-a-rare-and-horrifying-sight/