Denver’s Outdoor Warning Sirens: What To Do When They Sound:
The City and County of Denver has an outdoor warning siren system consisting of 76 electro-mechanical sirens (including nine at Denver International Airport). The sirens are tested on the second Wednesday of each month at 11:00 a.m.
Aside from the monthly tests, the siren system is only activated when a tornado has been spotted by trained observers, or when the National Weather Service has issued a Tornado Warning for Denver County
. A Tornado Warning means that a tornado has been sighted, or that a developing tornado is reported by trained spotters or indicated on Doppler radar. A warning is typically issued for a small area for less than an hour. Denver
’s siren system can be activated for either the entire county or for specific affected areas.