Mid-level clouds

Middle cloud of the layer type is referred to as altostratus and heap type cloud as altocumulus. They are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

(image embedded from NASA on 29 May 2009) Video embedded from YouTube on 10 April 2009
Altostratus (AS)
Altostratus is a layer type cloud that usually involves extensive coverage across the entire sky. It has a uniform blue or grey appearance. This type of cloud may be an indicator of approaching deteriorating weather. When the thickness of this type of cloud is substantial, the sun is not visible through it. However, in thinner portions, the sun may be vaguely visible but not with a halo. Unless associated with frontal activities or mountainous terrain, turbulence is not usually a common feature of this cloud. The thickness and altitude of altostratus means that icing can be a severe problem. Altostratus clouds are usually layered, with ice crystals at the top, ice and snow in the middle, and water droplets at the bottom. Any precipitation to sea level is generally light. However, in mountainous terrain precipitation may be moderate to heavy and may involve rain, snow or sleet.

Altostratus (image embedded from NASA on 27 March 2009)


Flat altostratus with just a bit of contrast visible (image embedded from NASA on 27 March 2009)


Altostratus with tree (image embedded from NASA on 27 March 2009)

Altocumulus (AC)
Altocumulus often appears as a layer of patches of rather flattened globular masses that may be arranged in groups, lines, or waves following one or two directions. Typically a portion of an altocumulus cloud is shaded, a characteristic which makes them distinguishable from the high-level cirrocumulus. The presence of altocumulus clouds on a warm and humid summer morning is commonly followed by thunderstorms later in the day. Turbulence is generally light unless associated with orographic rising or active fronts. If the cloud water content is high, icing can be light to moderate. However, generally icing is usually considered to be light in altocumulus. Precipitation of any significance is not common with altocumulus.

Altocumulus (image embedded from NASA on 28 March 2009)


Puffy, cotton-ball looking Altocumulus (image embedded from NASA on 28 March 2009)


Altocumulus with house (image embedded from NASA on 28 March 2009)

1. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION (2008).On-Line Cloud Chart. Retrieved from National Aeronautics and Space Administration on 20 March 2009.
2. UNIVERSITY OF ILLINOIS AT URBABA- CHAMPAIGN (2009).Cloud Types. Retrieved from University of Illinois at Urbana-Champaign on 22 March 2009.
3. WIKIPEDIA (2009). List of cloud types. Retrieved from Wikipedia on 20 March 2009.

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