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Precipitation
• To get precipitation, you first must cool the
air to the dew point:
• RECC: Rising Air Expands Cools,
Condenses
• So…..one sure way to get air to the dew
point is to lift it up
There are 4 primary ways that air
gets lifted in the atmosphere
1. A hot spot
Adiabatic means to
change temperature
by expanding or
compressing air
Typical cloud formation from hot spot
Clouds often form along
mountain ridges from
this type of lifting
2.
Clouds and rain fall on windward side of mountain
windward
leeward
desert
The next slide will
show dramatically
the windward/leeward
differences
Or 10ºC/km
Or 5ºC/km
Cascade Mtns.
Windward Side
Leeward Side
this happens all along
the equator
N. Trade Winds
S. Trade Winds
3.
cold front
Warm front
4.
When warm and cold air meet, the warm air
is lifted over the cold air
Types of Precipitation
• Rain: drops of water falling from sky
• Snow: ice crystals falling from sky
• Sleet: raindrops freeze to ice pellets while
falling from the sky
• Freezing rain: raindrops freeze when they
hit the ground or land on an object
• Hail: large ice balls that form during
thunderstorms
Warm rain in Belize, near the equator
is common in the late afternoon
Away from the tropics, rain often starts in clouds as snow flakes
snowflake
melts into rain
refreezes into sleet
If it is cold enough all the way down, the snowflakes
land on the ground as snow
If it warms up on the way down, the flakes may melt
into rain
If the rain freezes before it hits the ground it is sleet
if it freezes when it hits the ground it is freezing rain
sleet or freezing rain is determined by how long the
rain drop falls through sub-freezing temperatures
freezing rain is very
destructive
Hail
Hail commonly
forms in severe
thunderstorms