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What happens in CoMo when the twisters come

twister movie

 In this week's CoMo Explained we breakdown tornado prediction, the siren system and explain how 'Tornado Alley' works.

They're quiet unobtrusive until they're not: tornado sirens. About 80 of them dot Boone County with the majority of them in a few mile radius of downtown. This week we wondered--how do those sirens get turned on?

When it comes to the physical switch, the answer is easy: Columbia/Boone County Joint Communications handles that. Joint Communications is located right above the downtown police station on Walnut. They're the folks that handle 911 calls and dispatch emergency vehicles. Tornado sirens are are connected to a radio network that allows Join Communications to wirelessly control all Boone County sirens at once.

There's more than one way to decide when and how to flip the switch. A lot of storm and weather is monitored by the National Weather Service (NWS), a federal agency. These guys are keeping an eye on the radar to see if storms could be creating tornadoes. A large storm system may sometimes look a little tornado-like--that is, they can sometimes rotate the way a tornado does. But a storm like this won't just coalesce into one big tornado and "touch down." Tornado creation is a little more subtle than that. A tornado will more often that not be "spawned" off the edge of a larger storm system.

If the NWS things a storm could potentially create tornadoes, they'll issue a "Tornado Watch." Watches are fairly common and by themselves won't set off the sirens. Joint Communications will take note of the watch and seek more information. If the NWS issues a "warning" that means actual tornado formations have been spotted by eye or radar and that will usually be enough to flip the switch.

Occasionally, Joint Communications might act on local info, throwing the siren before an official warning comes from the feds. That information will usually come in the form of eye witnesses calling into 911 or the non emergency line. The city will want to double check on this info, of course, often calling up nearby patrol cars or fire stations to check. But they'll that info a lot more seriously if the caller is an official "spotter." Spotters are volunteers that receive free training by the NWS to know how to spot tornadoes and what to do. Some of them are ham radio enthusiasts that will actually radio in their information directly to Joint Communications.

Of course, the other reason to flip the switch is to test them. If you're in range you'll hear the sirens on the first Wednesday of every month at noon. Siren maintenance is important because Columbia is an old city and some of the sirens are 50 years old or more. When a siren doesn't respond right during a test, the city will dispatch a contractor: Blue Valley Public Safety. These guys specialize in fixing outdoor alert systems like tornado sirens. On average, the contractor will bill the city and county $37,000 to keep everything in working order. Check out the map below for siren locations.

One last note: in my research for the show I noticed that sirens can sound pretty wildly different from town to town. Maybe that's not surprising to some people, but this is the only siren-having town I've lived in and the differences are pretty stark to me.  Check out Columbia's sirens:


And compare those to Chicago's sirens:


I brought this up with the city, and while they couldn't really account for tonal differences in other cities, they did point out that the sirens rotate, which create different Doppler effects depending on where you are.  I've not tested this out, but it might be interesting to try during next month's test. Send us a video or recording of what the sirens sound like where you are! We'll play them on the show.

Stream or download the podcast above to hear more about how sirens work and hear about some of the worst twisters to come through Missouri. Find us on the iTunes store and leave a comment if you're a nice person. Tweet us @scottpham or @ryanfamuliner.

Credit City of Columbia
City of Columbia
A map showing the locations of tornado sirens around Boone County. Most sirens cover a radius of about a half mile.

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