“The night I stayed too late I was hunched on the fog staring spellbound at spreading, reflecting stains of lilac on the water. A cloud in the sky suddenly lighted as if turned on by a switch; its reflection just as suddenly materialized on the water upstream…“ - Annie Dillard, Pilgrim at Tinker Creek (1974)

Pair with: Cloud Writing

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In general, clouds are classified by their altitude and form, which relates to the cloud’s stability. Depending on its type, a cloud might insulate (warm) the surface beneath it, or cool it, by reflecting incoming sunlight.

Low-lying cumulus clouds puff along gently, indicating fair weather. They tend to have flat bottoms and rounded, lumpy tops. Wispy cirrus clouds show up high in the atmosphere, and an abundance of them may indicate the arrival of a warm front (and weather). Cumulonimbus clouds form near the ground and tower upwards. Also known as thunderheads, these clouds announce the arrival of serious weather – storms, tornados, hail, snow, and hurricanes.

Clouds form when the air reaches its saturation point. Warmer air can hold more water vapor; colder air less. At the saturation point, water vapor condense onto dust, pollen, or other condensation nuclei. Clouds can form as land-warmed air rises, over land masses (mountains), as pressure fronts collide, as cold air masses displace warmer ones, or at low pressure points. Eventually, when enough water condenses around a nuclei, the force of gravity pulls the ice or water back down to the planet, creating precipitation in the form of rain, hail, sleet, or snow.

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