High clouds (with a base at an altitude of more than 6 km): Cirrus Cirrocumulus Cirrostratus Medium-altitude clouds (with a base at an altitude of between 2 and 6 km): Altocumulus Altostratus Nimbostratus Low clouds (with a base at an altitude of less than 2 km): Stratocumulus Stratus Cumulus The largest cloud type of all extends vertically through all three altitude layers: Cumulonimbus