Lenticular (lee wave) clouds

The last few days I've been in the Yorkshire Dales area of the UK and was treated to a sight I'd not seen before - lenticular cloud formations over the tops of the higher hills in the Dales. These are sometimes called flying saucer clouds as this is just what they look like. These were all seen yesterday June 24th in the late morning. I only managed to photograph one (a poor example) as I was being driven and was unable to stop when the very best examples (really like flying saucers with nice sharp edges) were visible. A few hours later these had all disappeared. I expect these are quite common in areas like the Dales, but this was the first time I'd seen them.

For more information see http://en.wikipedia.org/wiki/Lee_waves