Weather Watch

Stunning clouds over SLO created by ice crystals and water vapor

A cumulonimbus cloud near Los Osos. The upper-half of the cloud is primarily composed of ice crystals and the lower half is made of water droplets.
A cumulonimbus cloud near Los Osos. The upper-half of the cloud is primarily composed of ice crystals and the lower half is made of water droplets.

A few weeks ago an upper-level low pressure system produced some wonderfully stunning clouds made of ice crystals, rain drops and plenty of water vapor.

You see, clouds are the condensation of invisible water vapor on very small nuclei from dust, volcanoes, pollen, forest fires, pollution from cars and factories, salt from ocean spray or sulfite particles from phytoplankton in the oceans.

So how can one tell which cloud is made of liquid drops or ice crystals or both?

To answer this question, let’s first take a quick look at cloud types.

Back in 1803, English naturalist and amateur meteorologist Luke Howard developed a simple classification system. Howard’s system used Latin words to describe three basic families of clouds: cirrus (“curl of hair”) cumulus (“heap or pile”) and stratus (“layer or sheet”). In other words, he divided clouds into three types: hair, heaps and layers.

Howard later went on to name any type of cloud that produced precipitation as nimbus (“cloud or violent rain”). Howard later refined his cloud classification system and divided hair, heaps and layers into four primary cloud groups by the height of the cloud base above the Earth’s surface.

These classifications include:

• High clouds are classified as cirrus, cirrostratus and cirrocumulus and form at altitudes from 16,000 to 43,000 feet at our latitude. They are primarily composed of ice crystals and can appear in a luminescent array of colors.



• Middle clouds are classified as altostratus and altocumulus, which form at altitudes from 6,500 to 23,000 feet. They are primarily composed of water droplets. However, they can also be composed of ice crystals.



• Low clouds are classified as stratus, stratus cumulus and nimbostratus, which form from just above the surface of the ground to 6,500 feet of altitude. When on the surface, they are referred to as fog. If the temperatures are cold enough, these clouds may also contain ice particles or snow.



• And last but not least, clouds with vertical development are cumulus and cumulonimbus. As the air rises thousands of feet into the sky, it cools and releases tremendous amounts of latent heat. This condition keeps the air rising inside the cloud and water droplets eventually freezes as they reach the cooler levels of the atmosphere. These types of clouds can on rare occurrences burst into the stratosphere!



In the photograph of the cumulonimbus cloud taken near Los Osos, the lower-half of the cloud looks like a heap or pile with sharp well-defined edges.

These characteristics usually point to a cloud composed of mostly of water droplets. On the other hand, the upper-half of this cloud appears to be wispy with fuzzy edges indicates that it’s made of ice crystals.

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