Precipitation 18.3 Brain Pop: Snowflakes Brain Pop: Rainbows

How Precipitation Forms Cloud droplets = < 20 micrometers. They must grow in volume by roughly 1 million times for precipitation to form.

Cold Cloud Precipitation Burgeron Process: Theory that relates the formation of precipitation to two physical processes – supercooling and supersaturation

Supercooled water: the condition of water droplets that remain in the liquid state at temperatures well below 0oC Water will freeze if it comes in contact with a solid object (freezing nuclei) Supersaturated air: the condition of air that is more highly concentrated than normally possible  relative humidity is > 100%

Warm Cloud Precipitation Collision-Coalescence Process: Theory that says large cloud droplets collide and join together with smaller droplets to form a raindrop. Opposite electrical charges may bind the cloud droplets together.

Forms of Precipitation The type of precipitation that reaches Earth’s surface depends on the temperature profile in the lowest few kilometers of the atmosphere

Drizzle: < 0.5 mm in diameter. Fall slowly & close together

Rain: >0.5 mm in diameter. Fall faster & farther apart

Snow: six-sided ice crystals Air temp < -5oC & air is drier  light fluffy snow Air temp > -5oC & air is wetter  thick clumps of snow

Sleet: When a layer of freezing air overlies subfreezing air near the ground, small particles of ice fall.

Glaze: When raindrops become supercooled (below 0oC) as they fall, then turn to ice on impact. A.K.A. freezing rain.

Hail: Ice pellets formed in cumulonimbus clouds Hail: Ice pellets formed in cumulonimbus clouds. Form layers of ice if carried upward by a strong updraft.

rain gauge: Instrument used to measure the amount of rainfall