Clouds and precipitation

A rain gauge measures the amount of rainfall at a place. In exams, remember it as the rainfall measuring instrument.

Clouds and fog are both collections of tiny condensed water droplets or ice crystals in the air. The main difference is their height: clouds usually form above the Earth's surface, while a cloud forming close to the ground is called fog. Option B is incorrect because both may contain water droplets and/or ice crystals; fog is not water vapour but condensed droplets. Exam tip: remember, ‘a cloud near the ground is fog.’

White cumulus clouds appear as separate, puffy heaps of cotton, often with relatively flat bases. Thin fibrous streaks are typical of cirrus clouds, while a uniform grey sheet is associated with stratus clouds. Exam tip: remember cumulus clouds as cotton-like heaps.

Dense water-rich clouds allow less light to pass, so they look dark. In exams, connect dark clouds with rain chances.

Water vapour cools into tiny droplets and forms clouds. In exams, remember condensation before rain.

Snowfall is solid precipitation because water falls as ice. In exams, connect snowfall with solid state.

Evaporation is water changing into vapour upward, not precipitation. In exams, keep precipitation and evaporation separate.

Nimbus clouds are related to rain-giving clouds. In exams, remember that nimbus means rain.

Rising air can cool and become saturated. In exams, link rising air with cooling and clouds.

In orographic rainfall, a mountain forces air to rise. In exams, connect air climbing a slope with orographic rainfall.

Convectional rainfall occurs when strong surface heating makes air rise. In exams, take afternoon heating as a clue.

Gravity pulls heavy droplets toward the ground. In exams, remember the relation between heavy drops and gravity.

Clouds connect evaporation, condensation, and precipitation in the water cycle. In exams, link clouds with the water cycle.

At height, lower temperature can form ice particles in clouds. In exams, link height and cold with ice particles.

Rain, snowfall, and hail are all water forms falling from the atmosphere. In exams, remember forms of precipitation separately.

Very small droplets can remain suspended until they grow larger. In exams, connect droplet size with rainfall.

Cyclonic rainfall is linked with low pressure and cyclonic air movement. In exams, take low pressure as a clue.

Nimbostratus clouds are widespread and can give continuous rain. In exams, link long-duration rain with nimbostratus.

Cumulonimbus clouds can grow greatly upward. In exams, connect vertical growth with storm clouds.

When droplets become large and heavy enough, they fall. In exams, remember this simple condition for rain.