Cool lenticular cloud forming over Mt. Cook. Photo taken end of december 2005, from near the Mueller hut, overlooking the Hooker valley. Note the amount of rubble on the Hooker glacier in the bottom of the picture.

Lenticular clouds are formed due to high winds, something of which I got a little taste that day when the wind picked up my cap and carried it some 50 meters before dropping it in a scree field. It really felt like someone grabbed it of my head. Thanks, took me half an hour to retrieve it.