Unusual Clouds - 25 Jun 2007290

Cumulonimbus (Cb)

Cumulonimbus is a type of cloud that is tall, dense, and involved in thunderstorms and other bad weather. The clouds can form alone, in clusters, or along a cold front in a squall line. Cumulonimbus is normally associated with heavy precipitation and thunder.

Other vertical clouds include: Cumulonimbus incus, Cumulonimbus calvus, Cumulonimbus with mammatus, Cumulus congestus & Pyrocumulus

Fog

Fog is a cloud in contact with the ground. Fog differs from other clouds only in that fog touches the surface of the Earth. The same cloud that is not fog on lower ground may be fog where it contacts higher ground such as hilltops or mountain ridges. Fog is distinct from mist only in its density. Fog is defined as cloud which reduces visibility to less than 1 km, whereas mist is that which reduces visibility to less than 2 km.
Most types of fog form when the relative humidity reaches 100% at ground-level. Fog can form suddenly, and can dissipate just as rapidly, depending what side of the dewpoint the temperature is on.

Stratus (St)

A Stratus cloud, coming from the Latin word meaning "spread out" is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide (these are termed Cumulus clouds). More specifically, the term Stratus (abbreviated ST) is used to describe flat, featureless clouds of low altitude (below 6500-8000 feet or 2400 meters) varying in colour from dark gray to nearly white. These clouds are essentially fog that is above ground level and are formed either through the lifting of morning fog or when cold air moves at low altitudes over a region. These clouds do not usually bring precipitation, although if sufficiently low in altitude to become fog, drizzle or mist may result.

Stratocumulus (Sc)

A stratocumulus cloud belongs to a class characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m (8,000 ft). Weak convective currents create shallow cloud layers because of drier, stable air above preventing continued vertical development.

Cumulus (Cu)

Altostratus is a cloud belonging to a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. Means "high spread out." Compare also with lower altitude stratus clouds.

High Clouds - Family A
These generally form above 16,500 feet (5,000 m), in the cold region of the troposphere. However, in Polar regions they may form as low as 10,000 ft (3,048 m). They are denoted by the prefix cirro- or cirrus. At this altitude water almost always freezes so clouds are composed of ice crystals. The clouds tend to be wispy, and are often transparent.

Cirrus

A cirrus cloud is a type of cloud composed of ice crystals and characterized by thin, wisplike strands, often accompanied by tufts. Sometimes these wispy clouds are so extensive that they are virtually indistinguishable from one another, forming a veil or sheet called "cirrostratus". Sometimes convection at high altitudes produces another form of cirrus called "cirrocumulus" a pattern of small cloud tufts. The name "cirrus" is derived from a Latin word meaning "wisp of hair."

View Cirrus Photo Gallery

Cirrostratus

Cirrostratus clouds belong to a class characterized by a composition of ice crystals and often by the production of halo phenomena. They appear as whitish and usually somewhat fibrous veils, often covering the whole sky and sometimes so thin as to be hardly discernible. These clouds are of high altitude (20,000–40,000 ft or 6,000–12,000 m). Compare cirrostratus with other stratus cloud formations at lower altitude: altostratus, nimbostratus, and low altitude stratus clouds. Cirrostratus clouds are signs that precipitation will follow in the next 12 hours.

Cirrocumulus

Cirrocumulus clouds are in high layers of sky and are formed horizontally. A Cirrocumulus is a high-altitude cirriform cloud, occurring at 20,000-40,000 ft or 6,000-12,000 m.

Cirrocumulus is formed from cirrus or cirrostratus clouds when they are warmed gently from below. The heating process causes air to rise and sink inside the cloud. This is why cirrocumulus is almost always associated with cirrus and cirrostratus. If this is not the case, the cloud is then an altocumulus.

View Cirrucumulus Photo Gallery

Unusual Cloud formations

These unusual cloud formations are less common in appearance than many of those shown above and are only often associated with more extreme weather conditions. This particular formation was photgoraphed by myself as a band of rain associated with a Low pressure over the country moved Northwards throughout the day passing Sandy in the evening of Sunday June 24th 2007.

View Unusual Cloud Photo Gallery

Virga

In meteorology, virga is precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is usually due to compressional heating because the air pressure increases closer to the ground. It is very common in the desert and in temperate climates. Virga can appear as straight lines or exhibit a hooked or curved form as the water or ice particles are blown by the wind as they fall. When seen from a distance, these streaks can be mistaken for funnels or tornadoes. I took these photos of Virga in the summer of 2006.

View Virga Photo Gallery