Cirrus Clouds

Cirrus Clouds

Feathery Ice Crystal Clouds ❄️

Altitude

20,000+ feet (6+ km)

Highest common cloud type

Composition

Ice crystals only

Never water droplets

Weather Signs

Change coming within 24 hours

Old weather adage rule

What Are Cirrus Clouds?

Cirrus clouds are delicate, feathery clouds composed entirely of ice crystals that form at very high altitudes (above 20,000 feet). They appear wispy and transparent, often called "mare's tails" due to their flowing appearance. Cirrus clouds are often the first sign that a weather change is approaching, as they typically precede warm fronts and weather systems by 24-48 hours.

Formation & Characteristics

Formation Process

  1. 1. High Altitude: Forms only above 20,000 feet where temperatures are below -40°F (-40°C).
  2. 2. Jet Streams: Often associated with jet stream outflow from upper-level weather systems.
  3. 3. Ice Crystal Formation: Water vapor freezes directly into ice crystals (deposition).
  4. 4. Wind Transport: Upper-level winds blow clouds into distinctive wispy patterns.

Key Characteristics

  • ✓ Appearance: Wispy, delicate, feathery strands
  • ✓ Color: White or slightly transparent
  • ✓ Texture: Fibrous, streaky patterns
  • ✓ Density: Very thin, sun clearly visible through
  • ✓ Movement: Drifts with upper-level winds
  • ✓ Composition: Pure ice crystals, no water droplets

Types of Cirrus Clouds

Cirrus Fibratus

Fibrous cirrus with a continuous, veil-like appearance covering areas of the sky.

  • • Covers large sky area
  • • Continuous appearance
  • • Often precedes storms
  • • Can completely cover sky

Cirrus Uncinus

The classic "mare's tail" cirrus with curved, hook-like appearance from wind shear.

  • • Hook or comma shape
  • • Indicates wind shear
  • • Beautiful formations
  • • Often points to weather changes

Cirrus Filamentosus

Thin, thread-like strands of cirrus clouds with very little structure.

  • • Thread-like appearance
  • • Very thin and delicate
  • • Sparse coverage
  • • Often isolated strands

Cirrus Castellanus

Cirrus with small turrets or towers indicating instability at high altitudes.

  • • Tower-like projections
  • • Indicates upper-level instability
  • • Severe weather possible
  • • Often in summer afternoons

"Mackerel Sky" & Weather Prediction

The old sailor's saying "Mackerel sky, mackerel sky - not long wet and not long dry" refers to patterns of cirrus clouds that indicate changing weather. When cirrus clouds appear in fish-scale patterns, significant weather changes typically occur within 24 hours.

Within 12 Hours

  • • Increasing cloud coverage
  • • Clouds lower and thicker
  • • Temperature may drop

12-24 Hours

  • • Precipitation likely
  • • Winds may increase
  • • Visibility decreases

24+ Hours

  • • Significant weather arrives
  • • May continue 12-24 hours
  • • Clearing follows passage

Key Facts About Cirrus Clouds

Physical Properties

  • • Ice crystals: 10-100 micrometers
  • • Liquid water content: 0.01-0.1 g/m³
  • • Cloud top temp: -40°F to -76°F
  • • Very thin, often translucent

Weather Impact

  • • No precipitation from cirrus alone
  • • First sign of approaching system
  • • Can be 24-48 hours ahead
  • • Marks jet stream location