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Altocumulus (from Latin altus 'high' and cumulus 'heaped') [1] is a middle-altitude cloud genus that belongs mainly to the stratocumuliform physical category, characterized by globular masses or rolls in layers or patches – the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. [2]
The altocumulus undulatus is a mid-level cloud (about 8,000–20,000 ft or 2,400–6,100 m), usually white or grey with layers or patches containing undulations that resemble "waves" or "ripples" in water.
When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 12 hours away. A thickening and lowering of cirrocumulus into middle-étage altostratus or altocumulus is a good sign that the warm front or low front has moved closer and it may ...
Mid-level stratocumuliform clouds of the genus altocumulus are not always associated with a weather front but can still bring precipitation, usually in the form of virga which does not reach the ground. Layered forms of altocumulus are generally an indicator of limited convective instability, and are therefore mainly stratocumuliform in structure.
The base of the cloud can form as low as 2,000 metres (6,500 feet), or as high as 6,000 metres (20,000 feet). They are very similar to cumulus congestus clouds, but at a higher level and with the cloud heaps joined at the base. Castellanus clouds are evidence of mid-atmospheric instability and a high mid-altitude lapse rate. [2]
A thickening and lowering of these high clouds into middle-stage altostratus or altocumulus is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours. Once the clouds have thickened to 2,500 metres (8,200 ft) from the earth’s surface, precipitation can begin to fall from heavy nimbostratus ...
Altocumulus stratiformis is the most common species of the Altocumulus genus of clouds. [1] They tend to form broad layers of individual, cell-like clumps, often separated from each other, though they sometimes can coagulate into a larger individual cloud. They often have a vertical extent of less than 500 m. [2]
The International Cloud Atlas or simply the Cloud Atlas, is a cloud atlas that was first published in 1896 [1] and has remained in print since. Its initial purposes included aiding the training of meteorologists and promoting more consistent use of vocabulary describing clouds , which were both important for early weather forecasting .