Tenea Fabray (Member 46,306) watched a towering storm cloud build over Des Moines, Iowa, US as the late-day Sun illuminated its billowing contours with shades of gold and cream.

The cloud was a Cumulonimbus and was on the threshold between this storm cloud’s two stages of growth: Cumulonimbus calvus (meaning ‘bald’ in Latin) and Cumulonimbus capillatus (meaning ‘hairy’). At this moment in its growth, the cloud’s cauliflower-like top was still fairly sharply defined, but the summit was beginning to spread and soften as its droplets froze into ice crystals. As the cloud top became more glaciated, the edges would turn wispy and Cirrus-like as it spread out into a huge icy canopy known as an incus (meaning ‘anvil’ in Latin). The dark streaks beneath Tenea’s developing incus hinted at falling precipitation, while its expanding upper region, fed by powerful updrafts within, cast a shadow below. ‘Coming in at sunset, it expanded and rotated,’ remembers Tenea, ‘and caused this massive cave-like moment to happen.’