Christine Foran (Member 58,407) tells us her friend Bruce is always looking at clouds and happened across these. He spotted them over Stokers Siding, New South Wales, Australia. They are a swathe of Altocumulus stratiformis perlucidus clouds curving across the blue, with flecks of Cirrus lurking alongside. Such a distinct cloud edge as this reveals very different air masses coming into contact with each other – usually as drier, sinking air nudges away a layer of moister air in which the Altocumulus clouds have formed. This is a sky divided as the cool quilt of cloud draws aside.