Ns compared with St neb op

(Section 2.3.6.6.4)

Nimbostratus is distinguished from Stratus nebulosus opacus (thick layer without distinct detail) by:

• Falls of rain, snow or ice pellets (Stratus has weak falls of drizzle, snow or snow grains)
• Usually evolving from an overcast layer of Altostratus, whereas thick Stratus usually develops in the absence of other low- or middle-level clouds