Cumulus humilis

Cumulus Humilis (Cumulus in good weather) look like dense bits of cotton and have a flatter (darker) base and well-defined contours that become less defined as they age and become more eroded. The sunlit parts have a bright white color.

They form in air masses with some instability, when at the place of their formation humidity is relatively low and temperature is relatively high. They often occur on clear days, when uneven heating of the Earth's surface causes floating air bubbles to rise by convection above the dew point level, causing droplet condensation.

The flat bases of the clouds define the dew point level and their tops the rising air limit. Vertical growth is small and there is rarely precipitation. They have daytime growth over the continent, developing until mid-afternoon and then decaying; over the coast or ocean often occur at night. They usually do not last longer than about 5 to 40 minutes.