Lenticularis clouds are recognisable by their distinctive, smooth disc or lozenge shapes. Kate Liosis (Member 55,164), who spotted these particular Altocumulus lenticularis, tells us that they often make an appearance in the autumn and winter around her home in Golden, Colorado, US.

Their name is Latin for a ‘lentil’, although they are often said to resemble flying saucers. They can be found downwind of raised terrain when stable winds are lifted into standing waves of rising and dipping airflows. Moist air can condense into cloud if it rises and cools enough at the crests. When the airstream contains alternating layers of moister and drier air, layered formations can appear like these ones, which are given the additional classification duplicatus. These saucers aren’t so much flying as neatly stacked – like someone’s helpfully done the washing up.