Dark blue cloudy sky

What is Altostratus?

A middle cloud type within the B family in the international cloud classification. These clouds consist of water droplets and sometimes ice crystals. In mid-latitudes, the cloud base varies between 15,000 and 20,000 feet. They can range in color from white to gray and bluish. Altostratus clouds can be fibrous or layered and may occasionally form a thick layer that obscures the sun and moon. The halo phenomenon is not observed with this cloud type. It is a good indicator of precipitation or a precursor to a storm. Virga-type clouds fall into this category. They are often formed by variations in low altostratus. They can cause light rain and snowfall. Subtypes of altostratus include opacus, precipitans, and translucidus.

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