The Globe and Mail: "Under certain weather conditions, sound can refract, and the focal point may be many miles away from the source.
The sound may actually be louder at the focal point (many miles away) than it is in the immediate vicinity of the explosion.
'Today is a typical day, with clouds, when you'll get a temperature inversion,' he said Wednesday. 'This is a classic situation where you have a focusing of sound. It might be further out than you think. It might even be in Vancouver.' "