Cloud types & what they indicate

A cloud's name tells you how it formed, and that tells you the weather. Break the name into its parts:

cumulo- / cumulus = heaped up by rising air (convection): unstable air, so bumps, showers, and good visibility in the gaps between the heaps.
strato- / stratus = spread out into flat layers: stable air, so a smooth ride, steady rain or drizzle, and often poor visibility.
nimbo- / -nimbus = carries rain (nimbostratus = steady rain; cumulonimbus = showers and thunderstorms).
cirro- / cirrus = high up, made of ice crystals.
alto- = the middle level.

Étage	Prefix	Genera	Made of
High	cirro-	Ci, Cs, Cc	ice crystals
Middle	alto-	As, Ac	water / ice
Low	(strato-)	St, Sc, Ns	water
Vertical	cumulo-	Cu, TCU, Cb	water, ice on top

Cirrus: wispy high ice-crystal cloud — **Cirrus (Ci):** high, ice crystals

Altocumulus: mid-level heaped patches — **Altocumulus (Ac):** middle level

Altostratus: grey mid-level sheet with a watery sun — **Altostratus (As):** middle, watery sun

Stratus: low featureless grey layer — **Stratus (St):** low, layered, stable

Stratocumulus: low lumpy layer — **Stratocumulus (Sc):** low, lumpy layer

Nimbostratus: dark low rain-bearing layer — **Nimbostratus (Ns):** steady warm-front rain

Cumulus: heaped fair-weather cloud — **Cumulus (Cu):** heaped, unstable

Cumulonimbus: towering storm cloud with an anvil top — **Cumulonimbus (Cb):** the thunderstorm cloud

Photos: NOAA, public domain, except nimbostratus (Onowhitu89, CC BY 4.0) and altostratus (W. carter, CC0), via Wikimedia Commons.

Cb (cumulonimbus) is the thunderstorm cloud: severe turbulence, icing, hail, lightning, and wind shear all at once (TC AIM MET).
Ns (nimbostratus) brings steady, non-stop rain or snow, the kind that comes with a warm front.
A halo around the sun or moon comes from the ice crystals in cirrostratus (Cs) and often warns that a warm front is on the way.

Intuition: heaps mean the air is turning over (unstable), so you get bumps, showers, and clear air rinsed out between them; layers mean the air is not rising (stable), so you get flat cloud, steady rain, and trapped haze.

Source note: the cloud families, étages, and the weather they signal are grounded in the FAA Aviation Weather Handbook (FAA-H-8083-28), a free public-domain text; the physics is universal and matches the Canadian material (equivalent to TP 9352). The TC AIM MET stays cited for the codes (METAR/GFA) and the Cb hazards (implies significant turbulence, icing, and low-level wind shear).

Trap: mixing up cumulo and strato is the big one (heaped and showery versus layered and steady). Do not read alto as "high": it means middle, and nimbo just means "rain", not a level of its own.

References

TC AIM MET
FAA Aviation Weather Handbook (FAA-H-8083-28)

PPL Tester

Cloud types & what they indicate

References

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