Did You Know: Anvil Clouds

Cumulonimbus incus ('incus' Latin for "anvil") is the upper portion of a cumulonimbus cloud that has reached a height in the atmosphere where the moisture condenses into ice crystals, and subsequently spreads into the characteristic flat, anvil-top shape as it straddles the lower stratosphere.

The cloud formation on the left in the picture shows an 'anvil cloud' in the making where the updrafts are drawing the moisture higher into the atmosphere. The cloud formation on the right shows a previous formation that reached the stratosphere and began to spread out, forming the characteristic 'anvil' shape. (This picture was taken looking west from the Gold Coast around 1pm on Thursday 22 November 2012)

This cloud formation usually is the result of strong updraft currents during the development of thunderstorms that can reach up to heights of between 40,000-60,000 feet (or 12-18 kilometres).

This photo taken in Canberra in 2008 shows a more developed cumulonimbus incus cloud formation. (Source: Wikipedia/Wikimedia Commons) 

They can also form into super-cell thunderstorms that often result in severe weather effects such as damaging wind gusts (downbursts and microbursts), large hailstones, heavy rainfall, lightning and sometimes (although rarely in Australia) tornadoes.

For more information about these clouds, check out these links:

Wikipedia - Cumulonimbus incus
BOM Storm Spotters Guide (Part 4)
weatherquestions.com - What is an anvil cloud?