Most of the victims of last year’s epic tornado outbreak in Alabama had at least one thing in common: They knew the storm was coming.

A year after the onslaught of dozens of twisters killed at least 250 people in Alabama and more elsewhere in the South, federal researchers are completing a study of who died and where they were when it happened. Among the conclusions so far: Nearly half of the people who died had been advised to take shelter. Indeed, most of them did.

But many of the tornadoes were so fierce that few structures were able to withstand them.

“These were catastrophic winds that could destroy pretty much anything in its path,” Cindy Chiu, an epidemic intelligence service officer, said in reporting preliminary findings this month at a Centers for Disease Control and Prevention conference in Atlanta.

The April 27, 2011, outbreak involved 62 tornadoes that stretched along ground-hugging tracks that covered more than 1,000 miles.

Fatalities were reported from central Alabama to far north Alabama.