Clouds from which Cirrostratus may form

(Section 2.3.3.5)

Cirrostratus may evolve from:

• Merging of elements of Cirrus (Cs cirromutatus) 
• Merging of elements of Cirrocumulus (Cs cirrocumulomutatus)
• Ice crystals falling from Cirrocumulus (Cs cirrocumulogenitus)
• Thinning of Altostratus (Cs altostratomutatus)
• Spreading out of the anvil of a Cumulonimbus (Cs cumulonimbogenitus)

Persistent contrails (Ci homogenitus) can, over a period of time and under the influence of strong upper winds, transform into Cirrostratus (Cs homomutatus). Occasionally, multiple persistent contrails (Ci homogenitus) may spread and give almost complete sky coverage of Cirrostratus.