Newly minted member Andrew Schied (Member 65,192) shared this towering cloud formation with us, sent by a dog-walking friend from Austin, Texas, US, unsure what it was.  

We can confirm this is the upper edge of a Cumulonimbus capillatus incus, a storm cloud with a fibrous, icy top and a distinctive anvil shape that forms when it hits the tropopause and can no longer rise so spreads outwards. It signals intense convection and is often linked to severe weather like lightning, hail, heavy rain showers, even tornadoes. The lumpy protrusions in the left edge are sometimes known as knuckles, showing that its upper region, or incus, is spreading rapidly. Flexing its fists to pack a punch, this is a cloud not to be messed with.