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Section 5

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precipitation

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rain

Rain droplets vary in size from 0.5 millimetres to more than 5mm in diameter. Rain normally falls from nimbostratus or altostratus clouds (see cloud chart).

drizzle

Drizzle droplets are smaller than 0.5mm and generally fall from stratus clouds or fog.

showers

Showers are precipitation that varies in intensity, generally falling from cumulonimbus or large cumulus clouds.

snow

Snow forms when water vapour turns to ice without first condensing into a liquid.

Snow flakes are composed of microscopic water crystals that cluster together in groups of 50 or more. When the temperature is low enough (say, minus 40 degrees), snow can fall from clear blue skies.

hail

Hail is formed when water droplets freeze in high, very cold clouds.

Hailstones grow bigger as they are coated with successive layers of ice. This can occur when they are pushed up and down through the atmosphere by strong updraughts and downdraughts. Hailstones can also get bigger when they bang into each other and stick, forming conglomerate hailstones.

Hailstones are usually only as big as a pea, but cricket ball-size hailstones have been known to fall in Australia, such as during the Sydney hailstorm of 14 April, 1999.

Coldfront Chart

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