Mammatus clouds are strange, pouchlike protrusions that can form on the underside of a thunderstorm's anvil-shaped cloud-top. They are caused by cold air sinking downwards and are often a sign of strong storms.  Some people describe them as like cow's udders, which made this pure coincidence seem so appropriate for a shot! Near Ynyslas, May 2009. Product number 050963b. Email me to enquire about this image: click HERE.