Editor's Note: A fan of the Mendota Heights Patch Facebook page asked why the sirens didn't go off Tuesday in Mendota Heights. Here's what we found.
Sirens went off in a number of Dakota County communities Tuesday night in response to severe weather—but not in Mendota Heights.
According to Mendota Heights Police Chief Mike Aschenbrener, that was no mistake.
In 2007, a method called “storm-based warnings” or “polygon warnings” became available. What that means is the area where sirens are to be activated is outlined on a radar map creating a “polygon” based on the longitude and latitude of where the storm path is.
In Dakota County, outdoor warning sirens are activated in the case of severe thunderstorm warnings, not just tornados. A severe thunderstorm warning indicates winds exceeding 58 mph, or hail ¾ inch in diameter or heavy rain.
By triggering sirens in the geographic area within the polygon, rather than the whole county, the total area receiving a false alarm is reduced, according to information from the National Weather Service.
If no area of Mendota Heights is in the defined path, no sirens will sound.
But if even a part of the city is included in a warning area, all of the five sirens in town will sound.
Sirens in West St. Paul also remained silent, according to Aschenbrener.
The Dakota Communications Center, the county’s 911-dispatch service, is responsible for activating the sirens based on polygon information from the National Weather Service radar.
Members of the Mendota Heights and departments are also trained weather spotters, and if they see something dangerous developing in the skies above them, they can also call in to activate the system.
So on Tuesday, while residents bordering Eagan or St. Paul may have heard their sirens go off, Mendota Heights neighborhoods remained quiet.