Weather Whys

By Texas A&M University —

Q: You often hear of “anvil clouds.” What are they?

A: Anvil clouds are common sights during spring and summer
thunderstorms and can occur almost all over the world, says Brent
McRoberts of Texas A&M University. “When a thunderstorm starts
developing, the large cumulus clouds reach heights where the moisture in
them is in the form of ice,” McRoberts explains. “The top of the cloud
expands and spreads out horizontally as the air bumps against the bottom
of the stratosphere, and it often forms an anvil-shaped cloud as it
expands. The central portion of an anvil cloud usually contains snow,
but this melts as it falls into the very warm air below.

“Q: How high do these anvil clouds reach?

A: McRoberts says airline pilots, who try to avoid such strong
clouds, often report them at levels of 60,000 feet or higher. “The rule
of thumb is, the higher these anvil clouds get, the more severe the
storm is that they contain,” McRoberts says. “They often produce heavy
rain and strong winds. Strong or severe storms often have a thicker
anvil appearance and you can often see a sort of boiling appearance in
the lower portions of them, meaning they contain very severe weather.”