Cirrostratus are thin and generally uniform clouds that are composed of ice crystals. These clouds are capable of forming halos. They are mostly located above 18,000 feet. When they are thick enough to be seen, they appear whitish, but usually have no distinguishable features. When covering the whole sky and often so thin as to be barely noticeable, this may indicate a large amount of moisture in the upper atmosphere.
Cirrostratus clouds can sometimes signal the beginning of a warm front and may help predict possible precipitation within the next 12 to 24 hour period.