Cloud Identification for Mariners
Classification and Observation of Clouds Provides Weather Warnings
Dec 25, 2007
Improved weather forecasting technology and ready access to weather forecast products gives present day mariners a great safety advantage over sailors of earlier generations. That said, weather can still be unpredictable at the local level and knowing about it is a mark of good seamanship. Identification and observation of clouds can provide clues to the severity of approaching storms. Watching the approach of a squall line with dark towering cumulonimbus clouds is a warning that a cold front is rapidly approaching. A blanket of nimbostratus or stratus clouds is a good sign of stable air and calm conditions.
Classification of Clouds - The English naturalist Luke Howard developed the first system of cloud classification to gain wide acceptance in 1803. Howard used four basic Latin terms to describe clouds as they appear to an observer on the ground, stratus for layer, cumulus for puffy, cirrus for wispy, and nimbus for rainy. All other clouds types are described using a combination of these Latin roots. In the end, there are ten basic cloud types described in four groups as being high, middle and low level clouds or clouds displaying vertical development.
High Clouds - These clouds form at above 6,000 meters (20,000 feet) in the middle and lower latitudes. There isn't much moisture in the air at these heights and the clouds are composed of ice crystals in thin layers.
- Cirrus (Ci) - Thin, wispy clouds that can have long feathery tails caused by high winds aloft.
- Cirrostratus (Cs) - Thin, sheet like clouds that can cover the entire sky. A sign that rain may come in 12 to 24 hours.
- Cirrocumulus (Cc) - Small, round cloud puffs that form individually or in rows. Cirrocumulus clouds formed into rows is known as mackerel sky in some regions.
Middle Clouds - These clouds lie between about 2,000 meters (6,500 feet) and 7,000 meters (23,000 feet). Middle clouds are composed mostly of water droplets and some ice crystals.
- Altostratus (As) - Gray cloud layers that can cover the entire sky. No apparent ground shadows differentiate As clouds from cirrostratus clouds.
- Altocumulus (Ac) - Gray, puffy cloud masses that be formed in waves or bands. These clouds can warn of afternoon thunderstorms.
Low Clouds - These clouds have bases below 2,000 meters (6,500 feet) above the earth's surface. Low clouds are predominately liquid water with snow or ice crystal in colder weather.
- Stratus (St) - A uniform gray cloud layer that can cover the entire sky. A layer of fog that lifts off the ground is a form of stratus clouds.
- Stratocumulus (Sc) - Lumpy, light to dark gray clouds that can form individually in patches, in rows or round masses. These clouds rarely produce rain or snow.
- Nimbostratus (Cb) - Dark gray clouds that are associated with continuous rainfall. Visibility is poor and precipitation is light to moderate.
Clouds with Vertical Development - In unstable air, cumulus clouds can tower to elevations of up to 15,000 meters (50,000 feet). The friction of moving air and the condensation of water droplets caused by these clouds release incredible amounts of energy in the form of violent winds and lightning.
- Cumulus (Cu) - Puffy clouds with round tops that are sharply outlined and have flat bases.
- Cumulonimbus (Cb) - A cumulus cloud that towers quickly is the hallmark of the classic thunderstorm. The top of these clouds can have flat tops caused by wind shears at high elevations. Cumulonimbus clouds can produce rain, hail, sleet, snow, and lightning, often simultaneously. The weather produced by these clouds is best avoided by small craft.
 |
 |
 |
 |
 |
