U.S. #3878i
2004 37¢ Altocumulus Castellanus
Cloudscapes
Issue Date: October 4, 2004
City: Milton, MA
Quantity: 8,336,000
Printed By: Avery Dennison
Printing Method: Photogravure
Perforations: Serpentine die cut 11
Color: Multicolored
“The moon is wading deep in snow,” is one of many sayings people used to forecast weather from the clouds.
Clouds form when moist air rises to a cooler altitude and condenses around tiny particles. Strong winds move the clouds around the world until the water falls as rain or snow.
In 1803, Luke Howard (1772-1864), a British amateur meteorologist, categorized clouds using Latin names. Modern cloud classification is based on his system.
The Latin cloud names describe their appearance. Layer-like clouds are called stratus clouds. Cumulus clouds are piled-up masses of white clouds. Cirrus clouds are curly white clouds.
Stratus and stratocumulus are low-level clouds. Mid-altitude clouds (alto-) are generally found between 6,000 and 20,000 feet. High altitude clouds (cirro-) are generally found above 20,000 feet.
Cumulus and cumulonimbus clouds may reach heights as great as 60,000 feet from their base. Beware when the top of such a cloud flattens out to the shape of an anvil. Then, it’s a thunderhead!
Once, people depended entirely on folklore to predict weather. Today, forecasters may use modern scientific instruments, but they still have to look to the clouds.