Weather Patterns Air Masses and Fronts

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Weather PatternsAir Masses and Fronts

• Section 17.1

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Air Masses
Arctic
Maritime polar
Continental polar
OK
Maritime tropical
Continental tropical

• Huge bodies of air that have similar temperature,
  humidity, and air pressure

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Fronts

• When an air mass moves into an area and interacts
  with other masses, it causes the weather to
  change.
• The boundary where air masses meet becomes a front

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Cold Front
Fast moving cold dense air pushes slow
moving warm air up Warm air cools and
precipitates
Since cold air masses move fast they can cause
abrupt weather changes (thunder
storms) After a cold front passes, colder, drier
air moves in bringing clear skies
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Warm Front
Fast moving warm air overtakes slow
moving cold air
Less dense warm air moves over dense cold air Can
produce rain or snow Area likely to become warm
and humid
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Warm Front
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Stationary Fronts

• Cold air and warm air meet but neither can move
  the other.
• Produces rain, snow or fog
• Can last for several days

Standoff between two air masses
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Stationary Fronts
Standoff between two air masses
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Occluded Front
A warm air mass is caught between two cold air
masses The denser air mass pushes the warm air
mass up The two cold air masses may mix
underneath the warm one The warm air mass is cut
off (occluded) from the ground The warm air
cools, condenses and may precipitate
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Cyclones Anticyclones

• Fronts become distorted because of things like
  mountains or jet streams (bending)
• Bending can cause swirls which can create low
  pressure centers

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Cyclones

• Swirling low pressure system
• Air pressure decreases as warm air rises
• Cooler air blows inward toward the low pressure
  area
• Coriolis effect causes the wind to spin
  counterclockwise in northern hemisphere
• Associated with clouds, wind, and precipitation

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Anticyclones

• High pressure systems
• Air swirls outward in clockwise direction in
  northern hemisphere
• Cool air moves downward and heats up lowering
  relative humidity
• Associated with dry, clear weather