Cloud Height and Cloud Types
Clouds are classified by their height in the atmosphere and appearance.
Clouds form at three height layers:
High Level Clouds form at 16,000 - 45,000 ft (5 - 13 km) - Cirro Prefix
Mid Level Clouds form at 7,000 - 25,000 ft (2 - 8 km) - Alto Prefix
Low Level Clouds form at land surface - 7,000 ft (0 - 2 km)
Clouds are also classified by appearance containing the following words:
Cirrus - wispy and thin.
Cumulus - Puffy appearance.
Stratus - Flat and/or layered.
Nimbus - Contain Precipitation.
| High Level Clouds : |
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Cirrus (Ci)
- Cirrus are high clouds composed of ice crystals that originate from freezing supercooled water droplets.
- Thin, wispy, often transparent.
- Usually indicates a change in weather within 24 hours.
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Cirrocumulus (Cc)
- High clouds composed of ice crystals.
- Small individual cloudlets in rows; no shading on lower surface.
- Usually indicate fair weather for the near future.
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Cirrostratus (Cs)
- High clouds composed of ice crystals.
- Thin, uniform appearance; often covering the whole sky. Halo around sun or moon may be seen.
- Usually indicate rain or snow within the next 12–24 hours.
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| Mid Level Clouds : |
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Altocumulus (Ac)
- Mid-level clouds composed of water droplets.
- Similar to Cirrocumulus but larger cloudlets with shading.
- If seen in the morning, prepare for a thunderstorm in the afternoon.
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Altostratus (As)
- Mid-level clouds composed of ice crystals and water droplets.
- Uniform grey appearance; can cover the entire sky. Sun or moon may appear fuzzy.
- Tend to indicate a storm in the near future.
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| Low Level Clouds : |
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Stratocumulus (Sc)
- Low-level clouds composed of water droplets.
- Appear as low patches or sheets of grey to white cloud, with rounded masses.
- Do not usually bring precipitation.
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Stratus (St)
- Low-level clouds composed of water droplets.
- Uniform greyish layer, often covers entire sky, may cover hilltops.
- Often bring drizzle or light snow.
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Nimbostratus (Ns)
- Low clouds consisting of droplets, raindrops, or ice crystals and snowflakes.
- Thick grey clouds with ragged base, sometimes covering the entire sky.
- Indicate rain in the very near future.
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Cumulus (Cu)
- Low-level clouds composed of water droplets.
- Puffy appearance, flat base, white or light grey.
- Indicate fair weather unless they grow vertically.
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| Vertically Developed Clouds : |
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Cumulonimbus (Cb)
- Vertically developed clouds composed of water droplets and ice crystals.
- Dark and very tall, can extend through all altitude levels and several miles wide.
- Usually indicate a storm: rain, hail, thunder, lightning.
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| Other Clouds : |
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Contrails
- Visible trails of condensed water vapor made by aircraft exhaust.
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