Why the Duke Emergency sirens test seemed so loud today.

The second Wednesday of every quarter throughout the year Duke power tests it’s network of audio emergency sirens. These sirens serve to warn residents of both nuclear emergencies, flooding from dam failures or water releases from their hydro power plants and even tornadoes in certain circumstances.

From Duke Power:

To ensure the sirens work properly, they will be tested at noon on the second Wednesday in January, April, July and October. The sirens will sound approximately three minutes, and no public action is necessary. Siren test dates for 2013 are:

  • January 9
  • April 10
  • July 10
  • October 9

This mornings test was particularly loud and heard at very long distances. Even I heard it in South Charlotte with all my windows closed in my house and the nearest siren to me is over 2 miles away. There was a good reason it was so loud and heard over such great distances. It’s something we call atmospheric audio ducting. It’s when we have an inversion or a warm layer of air just off the surface of the ground. It can trap and bounce the audio waves between it and the ground. Making them travel long distances and make the sound much louder. Thing of loud noises in a closed room versus outside. This happens often with distance thunderstorms or sonic booms when we have this stable layer of air near the ground.

(Credit Anthony Watts)

In this case the inversion which we still had at 11am-noon today allowed the siren sound to travel great distances and seem even louder than normal.

Here’s the NAM model sounding at 11am this morning:

1-9-2013 2-11-49 PM


So you weren’t crazy hearing the siren so vividly today blame it on ducting and the inversion. Listen to this if you really wan to be creeped out. This is video ducting from a distance thunderstorm.