(Ci)

high level cloud

thin, wispy, made of ice crystals

associated with fair weather

(Cs)

high level cloud (+5 km)

thin, sheet-like, halo around sun and moon

possible bad weather in 12/24 hours

(Cc)

high level cloud (+5 km)

rounded white puffs, found in rows

unsettled weather may be on its way

(Ac)

mid-level cloud (+2-5 km)

shallow, puffy, wave-like, made of ice and water

can appear in early morning or late evening

(As)

mid-level cloud (+2-5 km)

grayish/blue gray, can uniformly cover the sky, sun can be seen but no halo

usually seen in advance of storm

(Ns)

mid-level and vertical cloud (+0.5-5 km)

dark gray, wet-looking, sun completely blocked

produce light to moderate precipitation over a large area

(St)

Low-level cloud (>2 km)

uniform grayish cloud covering the whole sky, no precipitation, called fog on the ground

fog, drizzle, or mist if low enough

(Sc)

low-level cloud (>2 km)

low, lumpy, puffy, found in patches or rounded masses

drizzle, or light rain, passage  or approach of worse weather

(Cu)

low-level cloud (>2 km)

cotton balls or cauliflower

slightly developed means fair weather, moderately developed bring possible precipitation

(Cb)

vertical cloud (2-23 km)

towering appearance, anvil-shaped tops

thunderstorms