1. Clouds Based Above the Surface ( three classifications )
A. low cloud - bases up to 6,500 feet
a) SC - Stratocumulus - grey or whitish sheet of layer cloud with rounded masses or rolls and a wall defined base
b) ST - Stratus - grey layer cloud with a uniform, diffuse base, which may give drizzle or snow grains
c) SF - Stratus Fractus - small ragged patches of Stratus or fog that is in the process of dissapeting
d) CF - Cumulus Fractus - small, ragged ragged puffs of cloud, white in color. it is Cumulus cloud that is in the process of forming.
e) CU - Cumulus - detached cloud, generally white, dense and with a sharp outline. Has a flat base, rounded top and develops vertivally
f) TCU - Towering Cumulus - a CU cloud that has grown much larger ( vertical extent 10,000 feet or more). Sunlit parts are a brilliant white whle the base is usually dar and horizontal. Tops often look like cauliflowers.
g) CB - Cumulonimbus - a CU with considerable vertical extent (30,000 feet or more). Top part often takes the form of an anvil in later stages. It is responsible for all thunderstorms and lightning. Frequently accompanied by heavy rain and
h) NS - Nimbostratus - grey or dark grey and very thick layer cloud, usually associated with warm fronts. Continuous rain or snow
2. Middle cloud - bases 6,500 to 20,000 feet
a) AS - Altostratus - grey or bluish sheet of cloud with a smooth base, in places thin enough to reveal the sun vaguely
b) AC - Altocumulus - white and/or grey sheet of layer cloud with shading and composed of rounded masses or elements
c) ACC - Altocumulus Castellanuns - AC with protruding turrets or elements. Often a forerunner of thunderstorms
3. High cloud - bases above 20,000 feet
a) Ci - Cirrus - detached pure white clouds in the form of delicate filaments or strands of white patches or bands
b) CS - Cirrostratus - whitish layer cloud composed of tiny elements, like ripples of sand on a beach.
note: Unstable air results in clouds of vertical development (SU, TCU, CB) when one or more of the above forms of lift is present.
C. Surface Based Clouds or Fog
1. Radiation for
a) conditions which support formation
- clear skies
- moist air
- light winfs (less than 5 knots)
b) characteristics
- thickens at sunrise
- forms in low lying area first
- burns off after sunrise if no cloud cover moves in
- does not form over water
2. Advection fog
a) condition which supports formation
- warm moist air mocing over a cold surface
b) characeristics
- persistant if wind flow is unchanged i,e, wind direction must shift for fog to lift
- will form over water
3. Upslope fog
a) condition which supports formation
- generally found in the cold sector of a warm front where cold air bevoumes saturated from falling through it.
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