Starship Asterisk*

...strange clouds on Becca di Viou (Aosta Valley, Italy)

The picture was taken today, the 1st of July 2011, in Aosta, at 11:50 a.m.
(local). If you need, I have got a few number of pictures in which you can observe the
cloud motion.

http://en.wikipedia.org/wiki/Altocumulus_lenticularis wrote:

Lenticular cloud above northern Presidential Range, New Hampshire, USA

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<<Lenticular clouds (Altocumulus lenticularis) are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Due to their shape, they are often mistaken for Unidentified Flying Objects (UFOs).

Where stable moist air flows over a mountain or a range of mountains, a series of large-scale standing waves may form on the downwind side. If the temperature at the crest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds. As the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor. Under certain conditions, long strings of lenticular clouds can form near the crest of each successive wave, creating a formation known as a 'wave cloud.' The wave systems cause large vertical air movements and so enough water vapor may condense to produce precipitation. The clouds have been mistaken for UFOs (or "visual cover" for UFOs) because these clouds have a characteristic lens appearance and smooth saucer-like shape. Pilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence of the rotor systems that accompany them, but glider pilots actively seek them out.>>

owlice wrote:
The top one was taken before the bottom one; the cloud was expanding.

http://www.theairlinepilots.com/met/cirrusuncinus.htm wrote:
Cirrus Uncinus

Distribution: Worldwide.

Height: Above 16,500 feet.

Cause: Saturation of air mass at upper levels, combined with strong wind immediately below cloud level.

Associated Weather:
May indicate an approaching frontal system.

<<This often spectacular variation of cirrus cloud is also known as hooked cirrus (uncinus is the Latin for hook), or cirrus mares' tails, a reference to the cloud's resemblance to a horse's tail.

Cirrus uncinus forms in much the same way as other cirrus formations. However, its distinctive pattern of filaments is the result of a high-speed wind below the level at which the ice crystals form. As the crystals descend under the influence of gravity, this wind rapidly smears them across the sky, forming the distinctive, elongated, hooked shapes.

Like other cirrus clouds, uncinus is a result of high-level moisture, and is therefore often associated with the approach of a frontal system. Since it is also evidence of a high-speed, high-level wind, it may indicate the presence of a jet stream.

Normally, cirrus uncinus produces no significant weather on the ground, although snow showers may be visible immediately below cloud level. These usually evaporate well before reaching the ground and are therefore classified as virga.

As cirrus uncinus generally indicates the presence of high- speed winds, pilots often associate this cloud with turbulence. In most cases, however, the turbulence would cause little discomfort to pilots or passengers.

Excerpt from The Book " Weather "
Acknowledgement due: John W. Zillman, William J. Burroughs,
Bob Crowder, Ted Robertson, Eleanor Vallier-Talbot and Richard Whitaker.>>