Why did some cities hear tornado sirens on Monday, and some didn't?

Whether you heard a siren depended on where in the metro you were.
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If you're a resident of Hennepin County, you might be aware that a tornado warning was issued for the area on Monday evening.

A tornado did touch down near Maple Plain, with the warning expiring shortly afterwards.

There were a few confused comments from residents of the county directed at the National Weather Service, asking why they didn't hear any tornado sirens after the warning was issued.

Based on the comments on Twitter, residents in some parts of the county didn't hear a siren, while those in other areas did.

First of all, the National Weather Service doesn't have any control over the tornado sirens, as it had to point out repeatedly on social media Monday evening.

That decision is down to local emergency managers or local government. In Monday's case, Hennepin County Emergency Management says it activated warning sirens in Minnetrista, Maple Plain, Medina, Long Lake, Orono, Shorewood, Tonka Bay, Excelsior, Greenwood, Deephaven, Minnetonka, Wayzata, and Plymouth.

As Hennepin County explains it on Twitter, the decision on which sirens will sound is based upon the data the county receives from the NWS, with the tornado warning data "ingested by our software, and then automatically sounded sirens for any city with a siren inside the warning polygon."

So while there was a tornado warning affecting Hennepin County Monday, the NWS identified the red area below as the zone being particularly at risk, and as such sirens within this area were the ones that sounded.

The county's public alert and warning system also alerts people inside the warning zone automatically via messages to their smartphones.

As Hennepin County's Dan Anderson told BMTN, the majority of the approximately 290 sirens within the county are owned by either cities, or agencies like MSP Airport. 

However, Hennepin County Emergency Management has owns the siren control system, and chooses when to sound them and where.

The exceptions are "one or two" community-owned sirens that announce 9 p.m. whistles for curfew, Anderson said.

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