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Weather Fronts
What is a front?
Fronts are areas of rapid changes in
weather conditions and often sites
of unsettled and rainy weather
What is a Front?
 When different air mass meet, very little
mixing of the air occurs.
 Moves from West to East
 A sharp transition zone forms between the
air masses
Cold Front
Forms along the leading edge of a
cold air mass that is advancing
against a warmer air mass
The cold air mass is denser than
the warmer air ahead of it, so it
pushes against and under it like a
bulldozer.
Cold Front
This rapidly forces the warmer air
upward ahead of the front and
results in heavy precipitation and
thunderstorms.
After the passage of the front, the
temperature drops sharply and
the pressure rises rapidly
Warm Front
Forms when a warm air mass
overtakes a cold air mass ahead of
it.
Warm air is less dense so it rises
up and over the colder, denser air
Warm Front
 As it moves over the cold air, the
warm air expands and cools which
causes condensation to occur over
the wide, gently sloping boundary
 Results in thickening, lowering clouds
and widespread precipitation
Occluded Front
 Cold air masses move faster than
warm air masses and fronts because
cold air is denser and exerts more
pressure.
 If a slow-moving warm front is
followed by a fast-moving cold front,
the cold front will sometimes
overtake the warm front
Stationary Front
 Forms along the boundary between a
warm and cold air mass when neither
moves significantly in any direction
 Rain and clouds persist for a long
period of time until another air mass
comes along with enough force to get
it moving
Air Masses
 Large regions of air with fairly uniform
characteristics
 Identified by its average air pressure,
temperature, moisture content and
winds
 Characteristics are determined by the
geographical region over which it
formed.
 This is called its source region
Air Masses
The longer the air remains
stationary over a region, the
larger it becomes and the closer it
matches the characteristics of the
region
Air Masses
For example, a cold air mass
moving south out of Canada
will gradually become warmer
as it moves farther and farther
south
Arctic A
formed over extremely
cold, ice-covered
regions
Maritime m
formed over water,
moist
Continental c
formed over land,
dry
cA-dry, frigid and
formed north of
Canada
Polar P
formed over
regions at high
latitudes where
temperatures are
relatively low
Tropical T
formed over
regions at high
latitudes where
temperatures are
relatively low
mP-cold, moist
Formed over North
Atlantic, North
Pacific
mT-warm, moist
and formed over
Gulf of Mexico,
mid-Atlantic,
Caribbean, Pacific,
S. of Calif.
cP-cold, dry and
formed over
northern and
central Canada
cT-warm, dry and
formed over SW
United States in
summer
Wind
Wind is the natural movement of
the air along, or parallel to,
Earth’s surface
Result of uneven heating of the
Earth’s surface
Flows from high to low pressure
Jet Stream
 Very fast wind currents in the upper
atmosphere
 Does not follow surface winds
 Flows from West to East
 Influences development and
movement of weather systems
The Westerlies
west-to-east motion of the
atmosphere, centered over the
middle latitudes of both
hemispheres.
When there a storm in California,
it will most likely be in our area in
3-4 days