Aimed at giving people in the path of a potential tornado advance warning so they can take cover, a new reverse 911 service alerted many people in Warren County when severe weather approached Wednesday morning.“The system uses land lines to alert people when the National Weather Service issues a tornado warning for their area,” said 911 director Chuck Haston, noting people in the warning areas Wednesday morning were alerted by a phone call. “Outside the city where there aren’t any tornado sirens, there wasn’t really a way to do a mass notification before. The reverse 911 system provides us with a way to do a mass notification.”In the case of the pre-dawn storm Wednesday morning, residents with land lines in the warning area had an hour of advanced warning.