Download Air masses and fronts

Air Masses &
Fronts
High and Low Pressure Areas
• High pressure
causes air to sink
• Usually results in
several days of clear
sunny skies
• Air rises in low
pressure areas and
forms water
droplets
• Usually results in
rain and storms
What are the four types of air masses?
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Maritime Tropical
Maritime Polar
Continental Tropical
Continental Polar
Maritime Tropical
• Warm humid air masses from
oceans near the tropics.
• They form over the Gulf of
Mexico and the Atlantic
Ocean.
• In the summer time maritime
tropical usually bring hot
humid weather.
• In winter, a humid air mass
can bring heavy rain or snow.
Maritime Polar
 Cool humid air masses form
over the icy cold North Pacific
and North Atlantic oceans.
 The air masses affect the west
coast more than the east coast.
 In the summer they often
bring rain, fog, and cool
temperatures to the west coast.
Continental Tropical
 Hot dry air masses form
only in the summer over
dry areas of southwestern
and northern Mexico.
 Cover a smaller area than
other air masses.
 Bring hot, dry weather to
the south.
Continental Polar
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Form over central and
northern Canada and
Alaska.
Bring cool and cold air.
In winter they bring
clear, cool, and dry air to
most of northern America.
In the summer, storms
may occur when
continental air masses
move south and meet
maritime tropical that
move north.
How do air masses move?
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The prevailing westerlies are
the major wind belts in the
United States.
Prevailing westerlies push air
masses from west to east.
Fronts
A front is the boundary separating air masses
of different densities
 Fronts extend both vertically and
horizontally in the atmosphere
Fronts: FourTypes of Fronts
1. Cold Front: The zone where cold air is
replacing warmer air
• In U.S., cold fronts usually move from
northwest to southeast
• Air gets drier after a cold front moves
through
Examples
Fronts: Four Types of Fronts
2. Warm Front: The zone where warm air is
replacing colder air
• In U.S., warm fronts usually move from
southwest to northeast
• Air gets more humid after a warm front
moves through
Examples
Fronts: Four Types of Fronts
3. Stationary Front: When either a cold or
warm front stops moving
• When the front starts moving again it
returns to either being a cold or warm
front
Fronts: Four Types of Fronts
4. Occluded Front: Formed when a cold
front overtakes a warm front
• This occurrence usually results in storms
over an area
• In U.S., the colder air usually lies to the
west