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:









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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