I think.
It is a little odd living in a place where, when you hear thunder you question, at least briefly, if that is what you heard or if you should start worrying about heading people off to a shelter. Since the noise wasn't followed by a siren but by a phone call from a friend who was wondering the same I am certain we are safe, sound, and not under attack of anything more violent than a rainstorm.
Thunder means--
turn off the computer and pull out the plugs.