Turbulence
Heading for Heathrow from Jersey last night we were warned it might be a rough flight. About halfway the captain announced with a certain urgency that the seat belt signs were coming back on, and a few seconds later it was obvious why. Even at it's worst it was no doubt 'mild turbulence' in the great scheme of things, water bottles flying off tables ETC, and it only lasted a few seconds. But how did the captain know? Could he tell from the feel of the initially scarcely noticeable turbulence that it was going to get worse or was he warned of the bad patch of weather a couple of miles before we reached it?