Definition
High-altitude clouds composed almost entirely of ice crystals, typically forming above 20,000 feet. They appear thin, wispy, or fibrous and often take the form of streaks, sheets, or feathery patches across the sky. Cirriform clouds frequently signal moisture aloft and are commonly the first visible indication of an approaching warm front.
Plain English
Thin, wispy, ice-crystal clouds high in the sky. They look feathery or streaky and often show up before a weather change moves in.
Context Anchor
Seen in weather study and preflight weather checks when learning how clouds change as a warm front approaches.
Derivation
From the Latin 'cirrus,' meaning a curl, ringlet, or wisp of hair, plus '-form,' meaning 'in the shape of.' The name describes exactly what these clouds look like: curly, hair-like wisps stretched across the sky.
Why Pilots Care
They often indicate an approaching warm front that may bring changing weather, possible icing, or reduced visibility.
Grounding Statement
Picture thin white streaks high overhead that show the first signs of a larger weather system moving in.
Intuition Check
Cirriform does not mean one exact cloud type. It describes a thin, wispy cloud shape, most commonly associated with high clouds.
Example Sentence 1
On the morning of the flight, thin cirriform clouds streaked across the sky, hinting that a warm front was on the way.
Example Sentence 2
Cirriform clouds at altitude reminded the crew to check for possible ice on the wings later in the flight.