Download Precipitation - Cumulus Clouds

3/25/14 Supercooling of Water
Precipitation
—  Ice generally melts at 0oC but doesn’t necessarily
freeze. Tiny droplets of water can remain liquid at
temperatures well below freezing. This is called
“supercooling.”
—  Droplets can remain in liquid form until -40oC
Precipitation
—  Coalescence
— 
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— 
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Cloud droplets collide
Form larger droplets
Become too heavy
Fall
Precipitation Types
—  Rain
—  Collection of cloud droplets
—  Snow
—  Forms as ice crystals
—  Deposition (gas to solid)
—  Sleet
—  Rain freezes on the way
down
—  Freezing rain
—  Rain freezes on contact with
the surface
—  Hail
—  Convection currents carry
rain up and down through
freezing and nonfreezing air
Processes That Lift Air
—  Orographic lifting
—  Air is forced to rise over a mt.
—  Frontal wedging
—  Warm, less dense air forced over cool dense air
—  Convergence
Processes That Lift Air
—  Orographic lifting
—  Air is forced to rise over a mt.
—  Cools condenses
—  Clouds form
—  Then air descends
—  Cool air warms
—  Creates
—  Rain shadow desert
—  Converging winds force air upward
—  Localized convective lifting
—  Warm air rising
1 3/25/14 Processes That Lift Air
—  Frontal wedging
—  Warm, less dense air forced over cool dense air
—  Front- 2 different air masses collide
Processes That Lift Air
—  Convergence
—  Converging winds force air
upward
—  Warm Front
—  Faster moving warm air meets cold air
—  Warm air gets forced upward
Processes That Lift Air
—  Localized convective lifting
Stability
—  Warm air rising
—  Ability of an air mass
—  Hot sunny afternoon
—  Warm air pocket over
thunderstorms
to resist rising
cool surface
—  Heat transfers from the
warm air to the cool air
and surface
—  Warm air cools
—  Resists rising
Stability
—  Unstable air
—  Cool air and warm
surface
—  Warm air rises
—  Heats the air pocket
—  Air pocket rises
—  Cools, condenses, and
forms clouds
Atmospheric Stability
—  Stability
—  Stable Air
—  Parcel of air
—  Cooler than surroundings
—  Resists vertical movement
—  Doesn’t rise
—  Unstable Air
—  Parcel of air
—  Warmer than surroundings
—  Continues to rise
2 3/25/14 Atmospheric Stability
—  Different
—  Environmental Lapse Rate
—  Decrease in temp with altitude
—  Troposphere
—  5oC per 1000m
Stability and Daily Weather
—  Stable Air
—  Widespread clouds
—  Horizontal clouds
—  Little to no precip.
—  Adiabatic Rate
—  When air expands, it cools
—  When air is compressed, it
warms
—  Dry adiabatic rate
—  10oC per 1000 m
—  Wet adiabatic rate
—  Varies 5OC per 1000 m
What are the conditions necessary
for a T-storm to form?
—  Unstable Air
—  Towering clouds
—  Heavy precip.
What are the 3 stages of T-storms?
—  Moisture
—  Water vapor condenses
and forms clouds
—  Latent heat
—  Cumulonimbus clouds
—  Lifting Mechanism
—  Convective lifting,
orographic lifting, etc.
—  Unstable Air
—  Rising air
—  Cools, condenses, and
forms clouds
The Cumulus Stage
—  Cumulus Stage
—  Air rising – Updrafts
—  Latent heat
—  Condensation
The Mature Stage
—  Precipitation
—  Cools air – sinks
—  Downdrafts
—  Equal
—  Updrafts
—  Downdrafts
3 3/25/14 The Dissipation Stage
—  Downdrafts
—  Dominate
—  Rain tapers
—  Updrafts
—  Cutoff
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