Download Precipitation Precipitation on ground Frost is NOT frozen dew

10/13/2009
Precipitation on ground
Condensation if Dew Point is above 0o C
 Dew
 If DP is below 0o C

Precipitation
Types and Formation
Frost is NOT frozen dew…
Precipitation in the Air
Frost and Frozen Dew

Snow to water ratio approximately 10:1
10 cm of snow = 1 cm water
Snow – the most common form of precipitation
 Deposition forms snow flakes
 flake size >1mm to <2cm
 Smallest flake size at cold temperatures
Formation of Rain
Snow
 Cloud droplets rise above freezing level
(super-cooled water forms)
 Since ice crystals form more easily than
water droplets, super-cooled water
evaporates, then deposits and forms snow
 When snow falls through warm air it melts
and falls as rain
 Coalescence (Warm locations)
 small drops coalesce (collect) to larger ones
 BOTH - when ice or water drop gets too heavy
to stay suspended, it falls

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10/13/2009
Rime Ice
Precipitation – Rain

 Condensation
forms Cloud droplets
 droplets <.02mm (1/50 mm)
 droplets stay suspended in the air
 Liquid Precipitation
 Rain drops 5mm - .5mm
 Drizzle drops <.5mm
Super-cooled water in clouds freezes on
surfaces.
Other Liquid Precipitation

Other Frozen Precipitation
Virga
 Rain that evaporates before reaching the
ground

Sleet
 Rain falls through cold air (<0oC temp)
freezes before reaching the ground

Freezing rain (glaze ice)
 Rain hits freezing surface.
Precipitation Types
Freezing Rain
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T
T
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T
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l
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l T
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l T
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T
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T
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RAIN
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FREEZING RAIN
l
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T
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SLEET
T
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SNOW
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10/13/2009
Precipitation - Hail

Greensboro Hail Storm
Mother’s Day 2006
Hail – Solid
precipitation (ice)
formed in convection
currents in
cumulonimbus clouds.
 Each cycle a new
layer of ice is added
 Hail falls when
gravity is stronger
than the updraft.
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