Illustration of the various cloud types and the altitudes at which they form. The lowest cloud formations lie below 2km. These include cumulus, stratus, stratocumulus and nimbostratus. Between 2km and 5km we find altocumulus and altostratus. Lastly, at altitudes at and above 5km reside cirrus, cirrostratus and cirrocumulus. The largest cloud formations are cumulonimbus, which have their bases at low- to mid-altitudes and can tower above 12km high.