Air Masses

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Air Masses Fronts
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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

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What are the four types of air masses?

• Maritime Tropical
• Maritime Polar
• Continental Tropical
• Continental Polar

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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.

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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.

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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.

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Continental Polar

• 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.

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How do air masses move?

• The prevailing westerlies are the major wind
  belts in the United States.
• Prevailing westerlies push air masses from west
  to east.

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Fronts
A front is the boundary separating air masses of
different densities

• Fronts extend both vertically and horizontally
  in the atmosphere

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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
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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
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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

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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