WASHINGTON, Ill. — When a cluster of violent thunderstorms began marching across the Midwest, forecasters were able to draw a bright line on a map showing where the worst of the weather would go.
Their uncannily accurate predictions — combined with television and radio warnings, text-message alerts, and storm sirens — almost certainly saved lives as rare late-season tornadoes dropped out of the autumn sky.
Although the storms howled through 12 states and flattened entire neighborhoods within a matter of minutes, the number of dead stood at just eight.
By Monday, another reason for the relatively low death toll also came to light: In the hardest-hit town, most families were in church. ‘‘I don’t think we had one church damaged,’’ said Gary Manier, mayor of Washington, Ill., a community of 16,000 about 140 miles southwest of Chicago.
The tornado cut a path about an eighth of a mile wide from one side of Washington to the other and damaged or destroyed as many as 500 homes. The heavy weather also battered parts of Michigan, Wisconsin, Iowa, Missouri, Indiana, Ohio, Kentucky, Tennessee, West Virginia, Pennsylvania, and western New York.
Back in Washington, Daniel Bennett was officiating Sunday services before 600 to 700 people when he heard an electronic warning tone. Then another. And another.
‘‘I’d say probably two dozen phones started going off in the service, and everybody started looking down,’’ he said.
What they saw was a text message from the National Weather Service cautioning that a twister was in the area. Bennett stopped the service and ushered everyone to a safe place until the threat passed.
A day later, many townspeople said those messages helped minimize deaths and injuries.
‘‘That’s got to be connected,’’ Bennett said. ‘‘The ability to get instant information.’’
In Indiana, Taylor Glenna heard emergency sirens go off and received an alert on his cellphone. A friend also called to warn him the storm was nearly upon him.
Glenna went outside, saw hail and heard a loud boom. He ran to his basement just in time.
On Monday, he was surveying the damage on crutches after suffering a leg injury when the wind knocked his home off its foundation.
‘‘I would say we had pretty good warning,’’ Glenna said. ‘‘We just didn’t listen to it.’’
Forecasting has steadily improved with the arrival of faster, more powerful computers. Scientists are now better able to replicate atmospheric processes into mathematical equations.
In the last decade alone, forecasters doubled the number of days in advance that weather experts can anticipate major storms, said Bill Bunting of the National Weather Service.
But Bunting, the forecast operations chief of the service’s Storm Prediction Center in Norman, Okla., said it was not until Saturday that atmospheric instability, which can transform smaller storm systems into menacing ones, came into focus.
That is when information from weather stations, weather balloons, satellite imagery, and radar suggested there was more than enough moisture — fuel for storms — making its way northeast from the Gulf of Mexico.