Soon after a siren warned of a coming tornado on Friday evening, nursing assistant Linda Knapp took an elderly resident at the Monette Manor nursing home in Monette, Ark., to the bathroom. Then the twister struck, ripping the roof off the building and dislodging chunks of the wall.

Ms. Knapp recalled telling the man to grab a bathroom rail and hold on as tight as he could. She leaned over him to shield him from flying debris, and a piece of concrete struck her. A power outage plunged them into darkness, and water from rainfall...

Soon after a siren warned of a coming tornado on Friday evening, nursing assistant Linda Knapp took an elderly resident at the Monette Manor nursing home in Monette, Ark., to the bathroom. Then the twister struck, ripping the roof off the building and dislodging chunks of the wall.

Ms. Knapp recalled telling the man to grab a bathroom rail and hold on as tight as he could. She leaned over him to shield him from flying debris, and a piece of concrete struck her. A power outage plunged them into darkness, and water from rainfall or a sprinkler system soaked the floor.

Trapped by debris in the bathroom, Ms. Knapp said, she cleared away broken pipes and wreckage that were blocking the door and pried it open. She eventually got the man out and helped him toward an area near the nurses’ station where she could sit him in a chair and tend to him.

“The residents were talking to each other through the whole thing, asking each other if they were OK,” said Ms. Knapp, 69 years old.

Nursing assistant Linda Knapp was working at the nursing home when the tornado hit.

Photo: JOE RONDONE/USA TODAY NETWORK/REUTERS

The tornado was just getting started. After forming near the nursing home in northeastern Arkansas, the twister tore off to the northeast, carving a catastrophic path 230 miles long and as wide as three-quarters of a mile across Missouri, Tennessee and Kentucky over the course of about four hours. It was one of a series of tornadoes that killed at least 88 people and leveled swaths of towns.

Four days after the cataclysm struck, it is becoming clear that the early signaling systems put into place throughout the middle of the country, for the most part, worked as promised. People received text alerts and radio alerts from local officials and forecasters giving them enough time to shelter in place, as they have done for years during tornadoes. But the power, speed and duration of the tornado caught residents, businesses and cities by surprise and overwhelmed many of their safety procedures.

Images show the extent of damage at an Amazon warehouse and a candle factory after tornadoes tore through six states. As search operations continue, residents comb through debris for belongings and recovery teams face weeks of clearing. Photo: Adrees Latif/Reuters The Wall Street Journal Interactive Edition

The tornado’s estimated wind speeds of over 200 miles an hour would make it an EF5, the highest level on the Enhanced Fujita scale rating system. While meteorologists continue to analyze data on the tornado, its length was likely record-setting, preliminary results show. It sent debris 30,000 feet into the air, the cruising altitude of many passenger jets, and scattered prom photos, handmade quilts and wrapped Christmas gifts scores of miles away from the tornado’s path.

The twister rivaled the 1925 Tri-State tornado that killed 695 people as it traveled 219 miles across Missouri, Illinois and Indiana. A map of that storm’s path hangs at the National Weather Service’s Storm Prediction Center in Norman, Okla., said Bill Bunting, chief of forecast operations there.

“If you look through history, we’ve seen storms that have hit multiple towns before,” he said. “What we don’t see very often, perhaps only once before, is such an extensive path lengthwise, widthwise, and the number of communities affected.”

A rare confluence of weather conditions created it, Mr. Bunting said. First was the development of a supercell, an enormous weather system generating severe thunderstorms and rotating upward currents of wind. That combined with an unusually steady muggy environment, with temperatures hovering in the low 70s over the course of several hours. Moreover, no other major storms formed to disrupt the tornado’s formation or block its path.

“It was a sweet spot,” Mr. Bunting said.

Rick Sampson, owner of the Monette Manor nursing home, said he had been monitoring weather advisories when he saw the warnings. He called his staff around 6:45 p.m. to alert them.

Nurses shut protective fire doors and moved many of the 67 residents into hallways in the center of the building, seating them in chairs or wheelchairs. A few lying in beds that couldn’t fit through doorways remained in their rooms, where nurses drew hanging curtains around them, Ms. Knapp said. Staff handed out pillows to residents to cover their faces when the tornado hit.

The home of Tracy Overby in Dawson Springs, Kentucky.

Photo: Will Overby

Nurse

Barbara Richards, 57, looked out a window and saw debris and leaves swirling toward them. She rushed back to tell residents the storm was coming. Moments later, it struck.

Some wept through the ordeal. Others sang hymns while they waited for first responders to arrive. When it was over, one 94-year-old resident was dead, and several others were injured.

About 100 miles to the northeast, in south-central Kentucky, the tornado bore down on Graves County. George Workman, the county jailer, was home babysitting his 6-year-old granddaughter, Gracelyn, when he saw the news forecasting a powerful tornado would arrive at 9:19 p.m.

The 55-year-old had lived in rural Kentucky his whole life. In his experience, tornadoes petered out as they approached his community east of the Mississippi River, which tended to act as a natural barrier.

Widespread destruction of homes and businesses in Mayfield, Kentucky.

Photo: Tannen Maury/Shutterstock

Based on the dire forecasts, though, he decided for the first time in his memory to shelter in a closet. He strapped a baseball helmet on his granddaughter’s head and a football helmet on his own. It was 9:10 p.m.

“She was fine until I couldn’t keep calm anymore,” he recalled. “She saw the fear in my eyes. When she saw that, she couldn’t hold it together.”

Shaking and roaring

The house started shaking at 9:20 p.m., and a roar that sounded to Mr. Workman like a railroad lasted for at least a minute. When it was quiet again, he walked out into the backyard and saw the path the tornado had torn across an empty field.

Mr. Workman loaded his granddaughter into his truck and drove the 5 miles into Mayfield, the county seat, dodging downed trees and power lines. The courthouse wall had collapsed on the jail, which was built mostly underground. When he arrived, he heard that jailers from surrounding counties were already sending vans to help evacuate the inmates, none of whom were seriously injured.

A decimated neighborhood in Mayfield, Kentucky.

Photo: Brandon Bell/Getty Images

Soon after he arrived, Mr. Workman heard that the candle factory where seven of his inmates were working the night shift had been obliterated. He wouldn’t get word until the next morning that the inmates all survived, but their supervisor, Deputy Robert Daniel, was killed by collapsing debris while trying to push the last of his charges to safety behind a thick wall. All told, eight people died at the factory.

Mr. Workman said it hadn’t crossed his mind to keep the inmates at the jail that night. He had been working for years to get an employment program going, providing employees to a local company that needed them and a source of income for the inmates so they could pay fines and save up for after their release. Their first day had been Dec. 7, three days before.

“You never want to put your people in harm’s way,” he said, choking back tears. “Unfortunately, in this situation, it’s something we did, and you live with that guilt. We couldn’t have expected this.”

He said he remembered sitting in the yard as a child and watching tornadoes go down the fence line in the middle distance. “This one here was a different animal,” he said. “The force of it, and the fact that it never really seemed to leave the ground, and it was so massive….It was just ungodly.”

The tornado arrived in Dawson Springs, Kentucky, about 75 miles to the northeast, about an hour later.

Judy Roehr, 81, was watching TV when she saw news that a tornado might be headed toward that western Kentucky town of about 2,500 people. She wasn’t too worried. She had lived in her ranch-style house for nearly 50 years and had never had a tornado strike near her.

Basement retreat

Her husband was gone that night. As she had done during prior storm warnings, she grabbed her purse and flashlight and went into the basement. She figured she would wait a bit and then go back upstairs.

A sudden force catapulted her forward. She landed facedown on the basement floor and felt rain coming down. The foundation of her house had shifted, leaving the basement open to the elements.

Tracy Overby, right, at her home after the tornado roared through Dawson Springs, Kentucky.

Photo: Will Overby

As she lifted herself up, she saw neighbors with flashlights coming to help. Nearby homes, she said, were “just flattened, like sticks.” At her own house, the roof was gone, windows and doors were torn off and there were holes in the walls.

Soaking wet and cold, she climbed into her 2005 Chevy Impala. Her phone was gone, so she had no way to reach anyone. “I had a full tank of gas, so I spent the night in my car just running the heat off and on,” she said.

She didn’t sleep at all. All she could think about was her daughter, Tracy Overby, who lives just behind her and had been out that night.

Ms. Overby, 54, was about a mile-and-a-half away at her fiancé’s mobile home. “We were just holding tight to each other and praying,” Ms. Overby said. A big branch fell across the porch and trees were uprooted. They didn’t realize the extent of damage across town.

Early Saturday, Ms. Overby connected with her mother via another relative’s phone. Ms. Overby drove home that morning and was stunned to see dirt lots and concrete porches where full suburban homes used to be.

Three neighbors had died, including her friend Jenny Bruce. Ms. Bruce, a widow, had decided to ride out the storm in her home with her dog, a Shi Tzu, according to her friend and pastor Kathy Redden. A neighbor found Ms. Bruce lying in the backyard, and the dog was found roaming one street over.

Ms. Overby pulled up to her own house, which was missing a garage and several walls, to see her own dog, Piper, barking on the front porch.

Write to Arian Campo-Flores at arian.campo-flores@wsj.com, Valerie Bauerlein at valerie.bauerlein@wsj.com and Jennifer Levitz at jennifer.levitz@wsj.com