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WEATHER
Weather –
 the condition of the atmosphere at a certain
time and place.
 Created mainly
by uneven heating
of earth’s surface
Changes in Weather
 Changes in weather are caused by
movements of air masses, which are large
bodies of air that have the same
temperature and moisture throughout.
 An air mass gets is moisture and
temperature from the area over which it
forms called source regions.
 Example: an air mass that forms of the Gulf of Mexico is
warm and wet because this area (source region) is warm and
has lots of water that evaporates into the air.
Air Mass Moisture Classifications
 Maritime (m) – forms over water (moist)
 Continental (c) - forms over land (dry)
Air Mass Temperature
Classifications
 Arctic (A) or Antarctic (AA) – forms over the
poles (very cold)
 Polar (P) – forms over polar region (cold)
 Tropic (T) forms over tropics (warm)
 Equatorial (E)- forms over equator (hot)
Humidity
 The amount of water vapor in the air
 If Earths air didn’t contain as much humidity
as it does, our weather would be like that of
Mars: No clouds (except dust), no rain, sleet
or snow, no thunder and lightning, no fog.
 And, without all of this water in all of its
forms, Earth’s life, if there were any at all,
would be as hard to find as signs of life on
Mars.
Fronts
-occur when 2 air masses meet.
 Types of Fronts:
 Cold front
 Warm front
 Stationary front
 Occluded front
Cold front
 Cold front – a cold air mass moves under the
less dense warm air mass and pushes it
upward, away from the earth’s surface
creating a cooler climate.
Warm front
 – a warm air mass moves over the cold
gradually replacing the cold air mass creating
a warmer climate.
Stationary front
 – a cold air mass and a warm air mass meet
and nothing happens because the cold air
does not have enough force to move the
warm air mass. The climate associated with a
stationary front is much like a warm front.
Occluded front
 – a warm air mass is caught between 2 cold
air masses both of which push the warm air
mass upward. The climate has cool
temperature and large amounts of rain or
snow.
Front Symbols
Wind
 Is created by the uneven heating of the earth
 Hot air rises, cold air sinks and rushes across
land to replace the hot air (convection)
Jet Stream
 a current of fast moving air found in
the upper levels of the atmosphere.
Jet streams form along the upper air
boundaries of large masses of warm
and cold air.
 These winds not only steer storms,
but also help determine the locations
of areas of high and low air pressure
at the Earth's surface.