Prepared by: Troy M. Kimmel, Jr.
                    Lecturer, Studies in Weather and Climate
                    Manager, Weather and Climate Resource Center
                    Department of Geography, University of Texas at Austin

IMPORTANT NOTE:
Please note that cloud heights are a function of where you find the clouds.. lower latitudes (closer to the
Equator), the tropopause is found higher in the atmosphere, therefore clouds are found at greater heights. On the
other hand, the tropopause is much lower near the poles, therefore clouds are found at overall lower heights.
The height references below are applicable to the middle latitudes (and particularly, Texas).
 

High Clouds (At or Above 20,000 feet)

-Cirrus (Ci) Wispy streamers, waves or masses of mostly ice crystal (some supercooled water droplets) clouds usually at heights of 20,000 feet or more. Fair weather unless they thicken into altostratus (Ac). Referred to as "mares tales." Usually west to east with upper level (jet stream) wind.

-Cirrostratus (Cs) A stratified (thin sheetlike) layer of white cirrus clouds that often covers the entire sky. So thin that the sun and moon can be clearly seen through with "halo" effect (usually transparent to sunlight). Shadows are cast. Fair weather clouds unless they thicken into altostratus.

-Cirrocumulus (Cc) Very small cumulus puffs, usually smaller then size of end of thumb when held at arms length, at the cirrus level. Has rippled appearance and can occur individually or in long rows often covering only portions of the sky. These clouds can indicate instability at upper levels of the atmosphere. Referred to as "mackerel sky," since rippled appearance often resembles scales of fish.
 

Middle Clouds (6,500 to 20,000 feet)

-Altostratus (As) Gray to blue gray (never white) cloud usually covering the entire sky. Bases are between 8,000 and 12,000 feet. Sun may appear as a dull rounded disk with no shadows cast. Usually form in advance of storms that produce much widespread and continuous precipitation.

-Altocumulus (Ac) Gray, puffy, rounded masses of cumulus clouds with bases between 8,000 and 12,000 feet. Sometimes rolled out in parellel waves or bands with bases darker than other parts of the same cloud. Individual cumulus puffs should be about the size of the ball of your thumb when your hand is held at arms length. Referred to "rising castles" (called castellanus) indicate instability at mid levels of the atmosphere.
 

Low Clouds (Surface to 6,500 feet)

-Stratus (St) A uniform grey stratified layer of low clouds within 2,000 feet of the ground. Can cover portions of or the entire sky. Only light drizzle or light snow grains fall from true stratus clouds. Fog occurs when stratus clouds are in touch with the ground surface. Very uniform cloud bases.

-Stratocumulus (Sc) Low, lumpy cloud layer with bases from 3,000 to 5,000 feet. These clouds contain more water and the cumulus puffs are larger than altocumulus. Appears in rows, patches or in rounded masses with blue sky visible between cloud elements. Sometimes occurs with the spreading out of cumulus clouds later in the day. Color ranges from white to dark gray. Little or no precipitation expected. To distinguish from altocumulus, hold your hand at arm's length. Stratocumulus cloud elements will be larger than the size of the ball of your thumb up to about the size of your balled fist.

-Nimbostratus (Ns) A dark, gray wet-looking cloud characterized by more or less continuously falling precipitation (rain or snow) of light or moderate intensity (never heavy precipitation). It is not characterized by thunder, lightning or hail. Bases of nimbostratus is normally impossible to identify clearly (because of precipitation). No sun or moon visible through cloud mass.
 

Clouds of Vertical Extent (Surface to above 60,000 feet)

-Cumulus (Cu) A cloud in the form of individual, detached domes or towers that are usually quite dense and well defined. Characterized by flat bases with bulging cauliform like upper part. Generally fair weather clouds that look like cotton puffs. These clouds indicate rising air motions (convection). Bases are generally 5,000 feet or below. (Cumulus Humilis)

-Cumulus clouds when appearing as small and broken fragments with a ragged edge are referred to as "cumulus fractus."

-Building Cumulus (Cumulus Congestus) - Sometimes abbreviated as MOD CU in METARS/Surface Weather Observations

-Towering Cumulus - Abbreviated as TCU in METARS/Surface Weather Observations (Cumulus Congestus)

-Cumulonimbus (Cb) Large, towering (precipitating) cumulus clouds accompanied by thunder, lightning and rain. Bases generally between 2,000 (tropical environments) and 10,000 feet (more arid environments); tops as high as 60,000 to 70,000 feet in more severe storms. Cirrus clouds, at top of parent cumulonimbus cloud, can be carried hundreds of miles away from the parent cloud by upper level winds near the tropopause. From a distance, the top of the cumulonimbus may look like a blacksmith's anvil.

tmk 07/03/00