Thor and Patty Foss were driving back to their Clay Township mobile home March 29 when they noticed the sky growing dark and ominous.

"It was a strange color I've never seen before," Mr. Foss said. "I said to my wife, 'That looks like something a tornado could come out of.'!\p"

By the time the couple reached home, heavy winds had ripped the aluminum skirting off the bottom of their trailer and hail had broken one window and left dents all over the west-facing exterior.

Five miles away, a tornado had cut a 10-mile-long swath of destruction through Clay Township.

The couple admit they've always been interested in the weather, but the violent storm that hit their township March 29 really piqued their curiosity.

And so the couple went to Millersville University's Pucillo Gymnasium for the school's first-ever public weather awareness fair Sunday to learn more about how tornadoes work.

"I never fully understood why only certain homes got hit," Thor Foss said. "Why didn't it get everybody in that area?"

What the couple learned from representatives of the National Weather Service at Sunday's fair is that a tornado is a very narrow column of rotating air, which explains why the tornado that ripped through Clay Township left a path of destruction that was only about 200 yards wide.

There were homes and buildings just outside that zone that sustained no damage at all.

"What happened really was remarkable," Thor Foss said.

The idea for Sunday's fair originated with Matt Potter, a junior majoring in meteorology at Millersville.

After attending a "weather-fest" organized by the American Meteorological Society earlier this year, Potter told his school's chapter of the society that Millersville should have its own scaled-down version of the event.

"Everybody's interested in the weather, so I wanted to do something to get the public out," said Potter, who lives in Gilbertsville.

Besides the National Weather Service's booth, other attractions at the fair included a "green screen," which is used by television meteorologists all over the country.

People stood in front of a blank screen, and thanks to computer-generated graphics, on a nearby television monitor it looked like they were standing in front of weather maps.

There were several stations in the gym where meteorology students led or performed experiments showing how weather systems work.

In one area, children lifted a parachute and pulled it back down to demonstrate a low-pressure weather system — in which the air typically rises and storms are prevalent — and high-pressure systems — in which the air falls and the weather is usually fair.

Chris Sloop, a 1989 Millersville graduate, had a booth set up at the fair to talk to people about his WeatherBug system.

Sloop and four others founded the company in 1992, when they started building weather stations.

Through a network of 8,000 of these monitoring systems all over the country, WeatherBug provides real-time weather information to television stations, schools, government agencies and nearly 25 million visitors to www.weatherbug.com.

Sloop majored in physics and computer engineering at Millersville University.

He did not take any meteorology courses, but he said weather is something that fascinates him.

"I always loved meteorology," he said. "I used to walk by their door (at Millersville) and look in and think to myself, 'Man, that's pretty interesting what they're doing.'"

Email: preilly@lnpnews.com