After several days of strong winds, Mary Finch (Member 60,197) ventured out to walk her dog Piper in Englewood, Colorado, US and noticed huge pouches hanging from the clouds.

These are known as mamma, from the Latin word for ‘udders’. Dramatic examples of mamma are, like these, found in the vicinity of powerful Cumulonimbus clouds. They usually appear on the underside of the anvil-shaped canopy, known as an incus, that spreads out at the top of the storm cloud. Cool, dense air in the incus can sink into warmer air below, dragging cloud droplets or ice crystals down with it to form huge lobes of cloud.

There may be blue sky on the horizon, but the big Cumulonimbus right over Mary’s head may well have some weather to deliver in the form of sudden, heavy showers – perhaps even with thunder, lightning, and hail. But as every owner knows, a dog needs to be walked, rain or shine.