Hennepin County will be expanding its tornado warning zones from four to 20 this year in hopes that if fewer people hear sirens, they'll be more likely to respond when they do.
"This will add more credibility to the sirens," said Eric Waage, county emergency manager. "There will be less chance of people hearing sirens, stepping outside and seeing blue sky."
The fine-tuning of the system, in tandem with National Weather Service warnings that are now issued for areas that are independent of county borders, will trigger sirens separately in areas about the size of townships. Minneapolis will continue to be one siren zone.
The new setup will mean, for example, that if a tornado has been sighted heading for the east side of Brooklyn Park, sirens won't necessarily be sounded in Rogers, 15 miles northwest. Sirens will continue to be switched on by local emergency managers, in most cases automatically, in response to warnings from the National Weather Service.
At the same time, drivers soon will see printed warnings more frequently along roads, Waage said. The county is working with Clear Channel Communications Inc. to employ a half-dozen digital billboards to carry tornado warnings. It will also use smaller digital roadside signs.
About 75 percent of tornado warnings in the U.S. are false alarms, although lead times on legitimate warnings have been increasing. Advance warnings for all tornadoes now average 12.5 minutes, the Weather Service said. For the strongest tornadoes, it's 17.8 minutes.
The Hennepin County upgrade is an adaptation to a Federal Communications Commission requirement that the county increase some emergency signal capacities. It is being paid for by a $504,000 federal Urban Area Security Initiative Grant.
"We thought we'd seize the moment," Waage said.
