Cumulus clouds look like piled cotton and often signal calm, pleasant weather.

The longer version

Fair-weather cumulus clouds build upward as pockets of warm air rise, cool, and condense during the day. Their flat bases sit at the level where condensation begins, while their rounded tops mark how far each rising pocket travelled. The piled shape comes from separate bubbles of rising air stacking over time, each one marking a fresh surge of warmth from below.

They usually signal settled conditions because they need sunlight to form and only weak vertical growth to stay small. When the atmosphere is unstable and the updraughts keep going, the same clouds grow taller and darker, and pleasant weather gives way to showers.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.