This webpage describes the different cloud types and explains how they form. Cloud terms are in alphabetical order. Accessory cloud- A cloud that is dependent upon a larger cloud system for existence. Anvil clouds, wall clouds, and funnel clouds are examples of accessory clouds. Altocumulus- Middle level cumulus clouds. They are composed of liquid drops and have patches of clouds arranged in regular patterns. Altostratus- Middle level stratus clouds. They tend to be too high and thin to produce significant precipitation but they can overcast the sky and produce light precipitation. Anvil- Anvils are the ice crystal clouds blown downwind from the top of a cumulonimbus thunderstorm clouds. Cirrus- The general term for high clouds composed of ice crystals. They have a feathery and wispy appearance. Cirrocumulus- Patches within cirrus clouds that give the appearance of the mackerel sky. The patches are often arranged in a regular pattern. Cirrostratus- High clouds composed of ice crystal stratus. The sun will often shine through them. Halos and sun dogs can be produced as the sun shines through cirrostratus. Comma cloud- A low pressure cyclone will often have the appearance of a comma on satellite imagery. The low pressure center and warm front make up the head of the comma while the cold front makes up the tail. Cumulonimbus- A thunderstorm cloud that encompasses the lower, middle and upper levels of the troposphere. They form by a deep layer of rising positively buoyant air in the troposphere. Cumulus- The general term for vertically developing clouds. They have a lumpy appearance and develop within an unstable layer in which the cloud can build due to positive buoyancy. Fair Weather Cumulus- A cumulus cloud that develops in a shallow depth of unstable air. Stable air above the shallow layer of unstable air limits the growth of these clouds. The lack of deep vertical development prevents them from being precipitation producers. Fog- Fog is a cloud that has the base on the earth's surface. Fractus- Fractus are also known as scud and cloud tags. They are isolated low level stratus clouds that can often be seen around the base of thunderstorms. They often look unorganized and flow with the low level wind. Funnel cloud- The cloud produced from condensation from a rotating column of air. The funnel cloud is the visible portion of a tornado produced from clouds. A funnel cloud is not a tornado if the circulation is not in contact with the ground. Lenticular- Lenticular clouds are clouds that form above mountains that have a lens and flying saucer shape. They form as air is lifted to saturation over the top of mountains. Mackeral Sky- Cirrocumulus that look like fish scales. Mammatus- Mammatus are pouched shaped clouds that protrude downward from the thunderstorm's anvil. They form as negatively buoyant moisture laden air sinks. The cloud remains visible until the air sinks enough that the relative humidity falls below 100%. The portion that has a relative humidity of 100% remains visible. Mammatus tend to be most prominent in extremely severe storms but can occur when storms are not severe also. Mare's Tail- A term used to describe wispy cirrus. The cirrus can look like a horse's tail in the wind. Nimbostratus- A precipitation producing stratus cloud. They develop due to forced broad scale lifting of saturated air and can cover great distances. Most non-thunderstorm precipitation is produced by nimbostratus. Noctilucent cloud- Extremely cold clouds with very small amounts of tiny ice crystals. These clouds are located 75 to 90 kilometers above the surface and are rarely seen due to their extremely low moisture density. They are best seen when the sun reflects radiation off them when the sun is below the horizon before it rises and after it sets. They are also best seen at higher latitudes. The can range in color from blues to orange and red. Rope cloud- A rope-like band of clouds on satellite imagery often along cold fronts or other boundaries. Shelf cloud- A low ominous cloud reaching across the sky in associated with thunderstorm outflow. Stratiform / Stratus- The general term for horizontal clouds that develop due to forced uplift. They have a flat appearance and develop within a stable layer. Stratocumulus- A low level stratus cloud that has distinct clumps. They look like a combination of small fair weather cumulus and a low level stratus deck. Uncinus- They are hooked shaped cirrus clouds and are also called mare's tails. Wall cloud- A lowered cloud base within the updraft region of a supercell thunderstorm. The rapid lifting of humid air causes the cloud base to form at a lower elevation. Wall clouds will often rotate cyclonically. |