Nature Photos of the Week

May 30, 2007

Cloud Types!

Cumulonimbus calvus is a moderately tall cumulonimbus cloud which is capable of precipitation, but has not yet reached the height where it forms into a cumulonimbus incus (anvil-top).

 

Altostratus is a cloud belonging to a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darkers than cirrostratus. Compare also with lower altitude stratus clouds. Altostratus is caused by a large air mass that is lifted then condensed, usually by an incoming frontal systemand can be found over wide-spread areas. Altostratus clouds are potentially dangerous, because they can cause ice accretion on aircraft. Their altitude is from 6,500-20,000 feet.

 

A mackerel sky is an indicator of moisture (the cloud) and instability (the cumulus form) at intermediate levels (2400-6100 m, 8000-20,000 ft). If the lower atmosphere is stable and no moist air moves in, the weather will most likely remain dry. However, moisture at lower levels combined with surface temperature instability can lead to rainshowers or thunderstorms should the rising moist air reach this layer. There is an old saying, "Mackerel sky, mackerel sky. Never long wet and never long dry." The phrase 'mackerel sky' came from the fact that it looks similar to the markings of an adult king mackerel.

 

Lenticular clouds, technically known as altocumulus standing lenticularis, are stationary

lens-shaped clouds that form at high altitudes, normally aligned at right-angles to the wind direction.

Where stable moist air flows over a mountain or a range of mountains, a series of large-scale standing waves may form on the downwind side. Lenticular clouds sometimes form at the crests of these waves. Under certain conditions, long strings of lenticular clouds can form, creating a formation known as a wave cloud.