Cirrus

Definition

A genus of high cloud, composed almost entirely of ice crystals, appearing as detached white filaments, tufts or narrow bands. Cirrus has no shading and never produces precipitation that reaches the ground.

Field note

Cirrus is the leading edge of a frontal cloud shield: it is the first cloud you see and the thinnest part of the system. Estimate its coverage in oktas; rising coverage is the forecast.

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Cirrus: high ice, and the twenty-four hour warning

Cirrus is pure ice crystal at 6000 metres and above, and it is the earliest visible sign that something is about to change. Its wispy hooks and streaks look decorative, but they are the leading edge of the cloud system that will, in a day or so, be raining on you.

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Related terms

• Cirrostratus · Cirrostratus
• Fibratus · fibratus
• Uncinus · uncinus