Clouds of the troposphere 5–13 km
High clouds are mostly made of ice crystals. Cirrus forms delicate fibres, cirrocumulus makes small ripples, and cirrostratus spreads into a thin veil that can produce a halo around the Sun.
Thin ice-crystal fibres shaped by winds high in the troposphere.
Small white cloudlets often arranged in fine ripples, mostly made of ice.
A translucent ice-cloud veil; its crystals can produce solar and lunar halos.
2–7 km
Rising air cools, allowing water vapour to condense into cloud droplets. Altocumulus forms patches, altostratus spreads into broad sheets, and thick nimbostratus can bring persistent rain or snow.
Patches or rolls of cloud, often with shaded parts, in the middle troposphere.
An extensive grey cloud sheet through which the Sun may appear dimly.
A thick cloud layer that often produces widespread, sustained rain or snow; it can extend across several levels.
0–2 km
Low clouds usually have bases below 2 km. Stratus forms a grey layer, stratocumulus makes broad rolls, and cumulus grows upward. Cumulonimbus can tower through much of the troposphere.
Low rounded cloud masses joined into patches, rolls or a broad layer.
Clouds with flat bases and rounded tops, formed by rising buoyant air.
A deep thunderstorm cloud with a low base and a high, often anvil-shaped top. It can produce heavy rain, lightning and hail.
A low, fairly uniform cloud layer that may produce drizzle.
350 m
Water evaporates from the ocean and the land. Moist air cools as it rises over mountains, forming clouds and precipitation. Rivers and groundwater return water to the sea, completing the water cycle.
Clouds of the troposphere High clouds Middle clouds Low clouds Coast & mountains Cirrus Cirrocumulus Cirrostratus Altocumulus Altostratus Nimbostratus Stratocumulus Cumulus Cumulonimbus Stratus Cloud classification · WMO Troposphere 