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Air Masses & FrontsAir Masses & Fronts

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Explain how air temperature, moisture, wind speed and direction, and precipitation make up the weather in a particular place and time.

Describe how global patterns such as the jet stream and water currents influence local weather in measurable terms such as temperature, wind direction and speed, and precipitation.

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High and Low Pressure Areas

• High pressure causes air to sink• Usually means clear, sunny skies

• Air rises in low pressure areas and forms water droplets• Usually means rain and storms

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Air MassesThese are two types of air masses:

1. Cold Polar air masses

2. Warm Tropical air masses

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FrontsA front is the edge between two different air masses

Fronts spread both vertically (up and down) and horizontally (back and forth)

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Fronts: Four Types of Fronts1. 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

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Hint: These sharp points look like icicles. That will help me remember which symbol is the cold front.

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Fronts: Four Types of Fronts2. 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

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Hint: These bumps look like suns. That will help me remember which symbol is the warm front.

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Fronts: Four Types of Fronts3. 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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Hint: I have a stationary bike for exercising. I ride and ride, but it doesn’t go anywhere. Neither does this front. Notice that the warm air is pushing one way and the cold air is pushing the other way.

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Fronts: Four Types of Fronts4. Occluded Front: Formed when a cold front catches up to a warm front

This usually results in storms.

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Summary Four types of fronts:

1. Cold2. Warm3. Stationary4. Occluded

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Summary

Two types of air masses:

1. Continental Polar air masses2. Maritime Tropical air masses

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Summary HIGH PRESSURE • High pressure causes air to sink• Usually results in several days of clear sunny skies

LOW PRESSURE• Air rises in low pressure areas and forms water droplets• Usually results in rain and storms

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SourcesPalmer, Chad and Evans, David. May 20, 2005. Occluded fronts can

signal weakening of storm. Accessed 28 October 2005. http://www.usatoday.com/weather/tg/wofront/wofront.htm

Palmer, Chad and Kepple, Kevin. May 20, 2005. High-pressure systems brings sunny days. Accessed 27 October 2005.http://www.usatoday.com/weather/tg/whighp/whighp.htm

Palmer, Chad and Kepple, Kevin. May 20, 2005. How low pressure systems affect weather. Accessed 27 October 2005.

http://www.usatoday.com/weather/tg/wlowpres/wlowpres.htm

Weather World 2010, University of Illinois. No date of publicationgiven. Reading and Interpreting Weather Maps. Accessed 21

October 2005. http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml