Altocumulus
6,500 - 20,000 ft (2,000 - 6,000 m)
“When clouds appear like rocks and towers, the earth's refreshed by frequent showers”— Traditional weather rhyme
Altocumulus clouds are the middle children of the cloud family—not as dramatic as the towering cumulonimbus, not as ethereal as the wispy cirrus, but possessing their own quiet beauty that rewards those who take the time to look.
These clouds form in layers or patches of rounded masses, like cotton balls that have been gently flattened and arranged in rows. On summer mornings, they can create spectacular displays, catching the early light and painting the sky in shades of pink and gold.
The classic altocumulus pattern, with its regular rows of cloudlets, has earned it comparisons to everything from sheep in a field to the scales of a fish. When they appear on a warm, humid morning, keep an eye out—thunderstorms might be brewing by afternoon.
things worth knowing
- Altocumulus castellanus (the tower-shaped variety) appearing in the morning often predicts afternoon thunderstorms
- They can form through several processes including lifting of air masses and spreading of cumulus tops
- The individual cloudlets are typically the size of your thumbnail held at arm's length
- Altocumulus lenticularis (lens-shaped) are often mistaken for UFOs
weather wisdom
Morning altocumulus on a warm humid day can indicate afternoon thunderstorms