Cirrostratus
What is Cirrostratus?
Cirrostratus clouds cover all or
part of the sky in a sheet thin enough that the Sun or Moon are clearly visible
through them. When these clouds are present there is often a halo, a ring of
light, around the Sun or Moon. The halo is produced by the refraction or
bending of light through the ice crystals within the clouds. In some cases,
when cirrostratus clouds are nearly transparent, a halo is all that marks
presence. When these clouds are thicker, they appear as a milky white sheet
across the sky.
Cirrostratus clouds are formed by a large-scale, gentle lifting of moist air to great heights. This rising air is a result of convergence, the flow of winds inward toward an area on the surface.
Cirrostratus is thinner and lighter in color than altostratus. Another way to tell the two cloud types apart is that only cirrostratus allows enough sunlight to pass through to create shadows on the ground.
Snow rarely falls from cirrostratus clouds, and when it does, it usually takes the form of virga, meaning it evaporates before it hits the ground. A layer of cirrostratus clouds that’s growing thicker often represents the leading edge of a warm front. If a band of middle clouds shows up next, you can expect rain or snow in the next twelve to twenty-four hours.
Cirrostratus clouds are formed by a large-scale, gentle lifting of moist air to great heights. This rising air is a result of convergence, the flow of winds inward toward an area on the surface.
Cirrostratus is thinner and lighter in color than altostratus. Another way to tell the two cloud types apart is that only cirrostratus allows enough sunlight to pass through to create shadows on the ground.
Snow rarely falls from cirrostratus clouds, and when it does, it usually takes the form of virga, meaning it evaporates before it hits the ground. A layer of cirrostratus clouds that’s growing thicker often represents the leading edge of a warm front. If a band of middle clouds shows up next, you can expect rain or snow in the next twelve to twenty-four hours.