For days, she had been worried about the swollen Missouri River, which snakes through the city only blocks from her house.

“All we could think was flooding, flooding, flooding,” she said. “Then the sirens go, and it’s, ‘Get to your basement. The whole neighborhood’s destroyed.’”

Not long after the storm had roared through town, parts of the capital were cloaked in darkness, with the only illumination coming from police lights and cellphones.

Wayne Weldon, who is 75 and a double amputee, rode out the storm at home. When it was over, there was a hole in the roof in his guest bedroom, not far from where he took shelter. “I could see the sky,” he said.

Sharp-eyed observers noted that the storm that hit Jefferson City lacked the familiar ropy vortex shape associated with tornadoes. Instead, the tornado was a thick wide band, a shape that informal tornado watchers call a “wedge tornado.”

The shape, according to Michael Tippett, a professor of applied mathematics at Columbia University, suggests that the tornado was likely a large one. The tornadoes “that caused the most damage and are the most dangerous are the ones which are large and long-lived, and they have a long track,” Dr. Tippett said. These storms can last for tens of miles instead of hundreds of yards.

Meteorologists also said they could detect by radar that debris had lofted to nearly 14,000 feet.

“That sort of signature happens when we get bad tornadoes,’’ said Mr. Franks, the National Weather Service meteorologist. “These types of tornadoes are pretty rare.’’