photo #5395523

Lily Tschudi-Campbell (Cloud Appreciation Society Member 61,279) spotted this lace-like pattern in the sky over St. Paul, Minnesota, US. ‘I’ve been wondering what the cloud is,’ said Lily, ‘– if it might be a mamma cloud with unusual lighting?’ Mamma are cloud features that look like lobes typically hanging from the underside of a layer. At first glance, these do look like mamma, but we think this might just be a trick of the light.Rather than lobes of cloud catching the light as they hang down from a dark layer of cloud, we think the cloud levels are the other way around. We think the dark parts are a lower cloud surface with a lattice of holes through which can be seen a higher, brighter cloud layer above. If so, this would make the lower, darker cloud the form of Stratocumulus known as lacunosus, Latin for ‘having holes’. Such a lattice of holes results from sinking pockets of cold air, with the fringes of cloud around the holes forming where warmer air rises to replace the sinking. The brighter cloud above, appearing through the holes of the Stratocumulus lacunosus, looks to be the mid-level layer cloud Altostratus. Whether Lily spotted bright cloud through the holes of lacunosus or, as she first thought, bright lobes of mamma hanging down from a darker cloud, this is just one of the many ways the light plays tricks on us in the sky.