– Roberta Anton saw the monster cloud from 10 miles away, a dark beast that blotted out the world.

“It was black as sin,” said Anton, a North Mankato resident who was living near St. Peter on March 29, 1998. “I thought, ‘There’s gonna be trouble in that sucker.’ ”

Minutes later, a tornado with winds up to 175 mph ripped through St. Peter, carving a path of destruction that forever changed the face of this scenic river town about 70 miles southwest of the Twin Cities.

The twister was one of more than a dozen spawned that day by a freakish “supercell” thunderstorm that cut a 60-mile-wide swath across the southern Minnesota prairie. It hit St. Peter about 5:30 p.m. on a Sunday, destroying more than 200 homes, damaging hundreds more houses and businesses, and ripping thousands of trees — an estimated 90 percent of the city’s stock — from their roots.

Two people died and more than three dozen were injured in the massive storm — which, before hitting St. Peter, wiped out the tiny town of Comfrey, some 60 miles southwest, before heading northeast and battering the small towns of Le Center and Lonsdale. St. Peter alone sustained more than $120 million in property damage. The tornado was so powerful that debris from the city was found as far away as Rice Lake, Wis. — a distance of 125 miles.

Twenty years later, this city of nearly 12,000 residents on the banks of the Minnesota River is thriving. The town rallied and rebuilt, and later this week it will celebrate its resilience with a ceremony to thank those who helped the city recover.

“You’re defined by how you respond when you’re knocked down,” said Todd Prafke, the city administrator. “St. Peter got up, and we decided we would be better.”

March tornadoes are rare in Minnesota, so rare that before that fateful Sunday, only six other twisters had occurred in March in Minnesota’s recorded history.

In fact, the tornadoes that blew across southern Minnesota that day were among the earliest ever recorded in the state. Tornado season in Minnesota usually doesn’t start until mid- to late April. But 1998 was an El Niño year, when the recurring climate phenomenon warms the equatorial oceans and affects weather around the globe.

Observers at the National Weather Service started noticing unusual activity on their radar screens that morning. Wind from the south was pushing moist, warm air north, where it would collide with the cooler air in Minnesota.

Meanwhile, the jet stream, a superhighway of air more than 6 miles high in the sky, was acting strangely, splitting into several streams with different pressures.

It was a recipe for the perfect storm.

Storm trackers spotted the supercell forming over Sioux Falls, S.D., about 3 p.m. and sounded the warning as it moved east. The first reported tornado hit Nobles County in southwestern Minnesota about 30 minutes later, damaging homes near Lismore.

About 4 p.m., a “monster wedge” dropped out of the sky near Comfrey. At more than a mile and a quarter wide, it was so massive that people didn’t even realize it was a tornado, storm investigators said later. It looked more like a giant, black fog bank.

The immense twister, which contained at least three separate funnels, hit Comfrey with winds of more than 200 mph, causing so much damage that in the days after the destruction, some wondered if the town of 426 residents could survive.

Said one firefighter the next day as volunteers picked through the rubble: “It’s like a bomb went off.”

After leveling Comfrey, the monster sent another funnel cloud toward St. Peter.

Spring break had just begun at Gustavus Adolphus College, and only about 50 students were on the campus, perched on a hill high above downtown St. Peter. One of them was Glenn Kranking, who lived in the Swedish House on campus.

Kranking was in the house along with Elin Ahlden, a student from Sweden, and her parents, who were visiting. When the first siren went off, nobody knew what to do. Kranking was from the East Coast, where tornadoes are rare.

A second siren sounded a few minutes later. Kranking went outside with Ahlden’s father, and they were stunned by what they saw — a huge black cloud. When a third siren sounded about 5:30 p.m., the four hustled to the basement.

“The tornado was on us pretty quickly,” Kranking, who’s now the chair of Scandinavian studies at Gustavus, said last week. The dust in the air set off a fire alarm and the windows broke out in the basement. “You could feel the change in [air] pressure,” he added. The pressure constricted their lungs. That, along with the dust, made it hard to breathe.

The four huddled on chairs in a circle and wrapped themselves in an old blanket. They didn’t say a word as the twister raged above them and the fire alarm blared in their ears. Ahlden’s mother tried to comfort Kranking and her daughter by rubbing their backs.

Finally, after about two minutes that seemed more like a lifetime, the basement fell silent. They crept up the stairs.

Most of the two-story house was gone. The rest of the Gustavus campus was in shambles, too, with uprooted trees everywhere. Old Main and the college chapel both lost their spires, and a half-dozen buildings were damaged beyond repair.

Kranking, who worked for the college’s weekly newspaper, dug his camera bag from the wreckage and started taking pictures as he wandered through the devastation. Today, his photos make up the bulk of the historic record of the twister’s immediate aftermath.

The experience affected him for years, Kranking said. He especially had a hard time around Christmas, when the smell of cut wood and broken branches brought him back to the scene of the destruction.

“I had trouble around trees, too,” he said. “I needed to see the skyline. And I definitely take sirens seriously.”

St. Peter will remember the tornado with a 20th anniversary community ceremony Thursday. Amid the harrowing stories of riding out the storm in basements, residents also say the twister left positive change in its wake.

“Something like this shows that people really will take care of each other after a disaster,” said Barbara Fister, whose downtown home in a historic old firehouse was severely damaged. “They really care.”

Fister recalled that in the days after the tornado, local restaurants set up grills in the rubble-strewn streets and cooked free food for local residents and the thousands who poured into town to help.

“At their core, people really do have an impulse to help,” she said.

Prafke had started his job as St. Peter’s city administrator only four months before the twister. He, too, retains a vivid sense of the generosity shown.

“So many people offered help. It really was something,” Prafke said. “We’ve struggled with how to thank everyone. It’s not like we had everyone register.”

In the two decades since the tornado, St. Peter’s population has grown from 9,900 to nearly 12,000. The cost to rebuild has been estimated at more than $200 million and includes a new high school, community center and library.

These days, Prafke keeps a copy of the city’s emergency preparedness plan close at hand. Though it seems unlikely that the city could ever be hit again in quite the same way, he’s not taking any chances.

The resilient spirit spawned by the disaster is felt in the city to this day, he said. So is the sense of humor that helped residents weather their hardship.

“Now,” said Fister, with a grin, “every roof in St. Peter needs replacing at the same time.”