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.
A map of the proposed warning zones was expected to be available online Wednesday, accessible via www.startribune.com/a2091.
The number of sirens across the county will remain at 242, the densest coverage for any county in the state, Waage said.
Across the metro area, only one other county, long, narrow Washington, has more than one warning zone. It has two.
Ramsey County Emergency Management Director Judson Freed said his county, which is both the smallest and most densely populated in Minnesota, doesn’t have the money to upgrade right now. But the city of St. Paul, he added, recently upgraded its sirens so they can accommodate the technology behind the targeting.
Warning systems across the metro area vary in what they warn for. Most, including Hennepin and Ramsey, sound sirens to warn for tornadoes and straight-line winds of 70 miles per hour or greater. Dakota County sounds them for tornadoes as well as thunderstorms that carry lightning and hail.
The sirens can also be used to warn for emergencies such as chemical spills or nuclear incidents. In some rural areas, including some in Hennepin County, they might also be used to call volunteer firefighters.