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Clouds and Precipitation. 6.1 and 6.2. Clouds – How they Form. Clouds form when water vapor in the air condense to form liquid water or ice crystals Temperature at which condensation begins is dew point Above freezing it forms droplets Below freezing may form ice crystals
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Clouds and Precipitation 6.1 and 6.2
Clouds – How they Form • Clouds form when water vapor in the air condense to form liquid water or ice crystals • Temperature at which condensation begins is dew point • Above freezing it forms droplets • Below freezing may form ice crystals • Particles must be present for the water to condense on a surface (smoke, dust, salt crystals).
Cloud Types • Cirrus – wispy, feathery and form at a high altitude, mean fair weather. • Cumulus – cotton balls, form less than 2 km above the ground. Short cumulus clouds mean fair weather, but tall anvil like ones means thunderstorms. • Stratus – flat layers, spread out, gray color, may produce drizzle, rain or snow.
Precipitation • Common types include rain, sleet, freezing rain, snow and hail. • Rain must be at least .5 mm in diameter. Smaller than this is mist. • Measure rain with an open tube called a rain gauge (collects 10 times more than actual depth, so must divide by ten)
Types of Precipitation • Freezing Rain – rain drops fall and freeze when surface is cold. • Snow – forms when water vapor in cloud is converted directly into an ice crystal. • Sleet – raindrops fall through the layer of air below 0 degrees Celsius. Ice particles smallers than 5 millimeters in diameter. • Hail – Forms inside cumulonimbus cloud, each time the hailstone goes through another cold region, a new layer of ice forms on surface.
