You know when you crest a hill only to find there’s a bigger one to climb beyond? Anne Parmenter, a friend of Christoph Geiss (Member 47,439), went for an early morning hike in the hills around Bartlett, New Hampshire, US and saw the snow-covered slopes seemed to extend right into the sky.

This smoothly curved formation is a Stratocumulus lenticularis cloud, the right end of which is rising in a peak by an unusual atmospheric movement known as Holmboe instability. That’s when the density and flow of the air at different layers cause vertical eruptions like this to develop along the tops of clouds. It’s a very rare occurrence that Anne was lucky to see – and lucky not to have had to climb.