Meteorologists concede that when it comes to predicting the random violence of severe storms and tornadoes, the most important forecasting tool is luck itself.
And in northern Alabama and Georgia, where several storm systems generated between 20 and 30 tornadoes Sunday, "there was a lot of bad luck," said Joe Wheeler, a meteorologist in the Birmingham office of the National Weather Service.
The tornadoes were not particularly powerful, Mr. Wheeler said, they "just happened to hit the right spot." They struck early in the day; tornadoes usually occur around 3 p.m. or 4 p.m., when the accumulated heat of the day causes rising air currents that become twisters.
The county that took the greatest force of the storm, Cherokee County, Ala., is a poor, rural one without an extensive warning system.
"Unfortunately, they have little in the way of a warning system there," said Lee Helms, the operation chief of the state Emergency Management Agency for Alabama, who said that progressively more severe storm alerts were issued on radio and television.
Tom McMahon, the press secretary for Sen. Howell Heflin, D-Ala., said the county was in the process of applying for money from the Federal Emergency Management Agency for the installation of warning sirens throughout the area and for giving nursing homes and schools tone-alert radios through which the National Weather Service could warn of dangerous weather.
The meteorologists responsible for forecasting the weather in the region said they were pleased with their performance.
"We anticipated the general threat the day before," said Jack E. Hales, the lead forecaster at the Severe Storm Center, which monitors severe weather around the nation. "But predictions are not as difficult as getting the warning out about them."
The areas covered are large, and the actual areas of destruction are comparatively small and cannot be pinpointed, Mr. Hales said.
"Tornadoes can range from brief touchdowns to the killer kind that go along the ground for many miles," he said. He added that with today's advanced technology, the best that forecasters can do is give 30 minutes warning to large parts of a state where they believe tornadoes are very likely.
The first indications of severe weather -- a mass of very cold dry air running up against very warm, humid air -- appeared Saturday morning and the center issued an "outlook for severe storms," Mr. Hales said. The outlook was upgraded to a "severe storm watch" Sunday morning, which was broadcast on radio and television in parts of several states.
Mr. Wheeler said the storm watch became a "tornado warning" some 15 minutes before a tornado actually hit the Goshen Methodist Church in Piedmont, Ala., at the southern edge of Cherokee County, killing 20 people.