News | January 5, 2015 11:25 AM

Outdoor Warning Sirens Explained

On Sunday, January 4 at 11:36 AM, the National Weather Service in Charleston placed Chatham County under a Tornado Watch. The Watch was elevated to a Tornado Warning for parts of the county based on weather radar of the storm system, thus simultaneously activating CEMA's Outdoor Warning Sirens.

 The sirens are linked to a system called WeatherWarn, which was purchased entirely through a federal grant in 2013. WeatherWarn is linked to NWS warning products based on radar to activate sirens and notify the public at the exact moment a storm changes, saving valuable time when seconds count. To eliminate confusion, CEMA moved from an all-county warning notification system to a polygon notification pattern, only activating sirens in the path of a storm based on live radar data.

The first siren was activated at 3:04 PM, ran for three minutes and then ran again at 3:19 PM. WeatherWarn is designed to move siren activation patterns with the storm in real time. The program is so sophisticated, it will deactivate sirens once the threat has passed. This would be why some county residents did not hear the warning sirens. While a tornado watch was issued for the entire county, only those areas within the warning pattern were issued sirens. It is important to remember that the warning sirens are designed to be heard outside. This was the first automatic siren activation due to a tornado warning with the new WeatherWarn Program.

Below is a  snapshot of the activated sirens and the warning polygon. As you will see, the yellow indicates that the entire county is in a watch. The boxes represent siren sites and those outlined in red were activated in the warning. 

Siren Activation 01-04.jpg

Last Updated: January 5, 2015 11:33 AM

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