OUTDOOR SIREN ACTIVATION
Counties and cities own the sirens, and therefore decide how and when to activate them. The National Weather Service does not sound them.
There are many different policies regarding siren activation that are used by the various cities and counties. Some will activate sirens across the entire county for tornado warnings only. Others will activate sirens countywide for tornado warnings and all severe thunderstorm warnings. Some will activate sirens across the entire county for tornado warnings and severe thunderstorms that have winds of at least 70 or 75 mph. Others will activate sirens only for portions of counties. Local officials may also sound the sirens anytime they believe severe weather is a threat, even if there is no warning from the National Weather Service.
Sirens normally sound for about three minutes, and then go silent. Some jurisdictions may repeat siren activation every few minutes and there is no such thing as an "all-clear" for storms.
Outdoor warning sirens are exactly that, they are meant to be heard outdoors. When sirens are sounded they are to alert people outside of an impending severe weather event. It is recommended if you hear the sirens immediately stop what you are doing, go indoors and tune into your favorite radio or tv station for further details or seek shelter immediately.
To receive severe weather warnings indoors, Emergency Management and the National Weather Service recommend the purchase of a weather radio, which can be found on-line and can be purchased from local electronic stores. These radios can be programmed for your specific County and can sound for a variety of weather events.