What is an air mass?A large body of air having nearly uniform conditions of temperature and humidity at any given altitude.

• Warm air forms over tropical regions near the equator. • T- Tropical

• Cold air forms over polar regions. P- Polar

• Wet air masses form over water m- maritime

• Dry air masses from over land. c- continental

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• Moisture content is noted by the first letter.

m – maritime – wetc – continental – dry• Temperature is noted by the second

letter.P – polar – coolT – tropical - warm

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Types of Air masses• Continental Polar (cP) , “cold and dry”

–closer to the Poles over land-locked regions.• Continental Tropical (cT), “warm and dry”

–closer to the Tropics over land-locked regions.

• Maritime Polar (mP), “cold and damp”–closer to the Poles over water.

• Maritime Tropical (mT), “warm and humid”–closer to the Tropics over water.

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FrontsThe advancing edge of a mass of cold or warm air. front- the area where two air masses meet and do not mix (from military language meaning a battle area where opposing armies meet to fight)A front always causes a change in weather because the air masses that meet do not mix and their different densities and air pressure produce wind, clouds and temperature changes.

• A front is a boundary between air masses.Four types of fronts and map symbolsThe directions that the bumps face is the direction the front is moving.

1. Cold front

2. Warm front

3. Stationary front

4. Occluded front 10

When a fast moving cold air mass runs into a slow moving warm air mass and the thicker cold air slides under the lighter warmer air.

• Bring thunderstorms, rain or snow.

• Most tornadoes develop from thunderstorms on the edge of a cold front.

• Cold front followed by sunny cooler drier air.

• http://www.mesoscale.iastate.edu/agron206/animations/05_cnWfronts.html 12

What will happen if the warm air mass contains only a little water vapor?

• Warm air with little water vapor may be accompanied by ONLY cloudy skies.

• If there is a lot of water vapor in the warm air, heavy rain(thunderstorms)or snow may fall.

When a moving warm air mass collides with a slowly moving cold air mass and the warm air moves over the cold air.

If warm air is humid, showers and rain fall along the front. In winter warm fronts can bring snow.• If warm air is dry, scattered clouds form.• Because warm fronts move more slowly

than cold fronts, weather may be more foggy or rainy for several days.

• After a warm front passes, the weather is likely to be warm and humid.

15http://www.mesoscale.iastate.edu/agron206/animations/05_cnWfronts.html

Stationary FrontsWhen a cold air mass and warm air mass meet, but neither air mass has enough force to move the other air mass.

• Many days of cloudy, wet weather.

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http://www.youtube.com/watch?v=VwI1NmESxss

When a warm air mass is caught between two cooler air masses and the thicker cold air masses move underneath the thinner warm air mass and push it upward.

• Brings cool temperatures with large amounts of rain or snow

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http://www.youtube.com/watch?v=4gc7puH279s

Cold Front, Warm Front and Occluded Front Animation

• http://www.phschool.com/atschool/phsciexp/active_art/weather_fronts/

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=visualization

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1. Describe a maritime polar (mP) air mass, in terms of moisture and temperature.

2. What is the name of an air mass that forms over water?

3. What is the name of an air mass that forms over land?

4. What is the name of an air mass that forms in a cold region?

5. What is the name of an air mass that forms in a warm region?

6. Describe a continental tropical (cT) air mass, Moisture and temperature.

Quiz

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Quiz7. The boundary between two air masses is called a

______________________.

8. A cold air mass meets and pushes a warm air mass out of the way. What type of front am I?

9. A warm air mass is trapped between to cold air masses. What type of front am I?

10. A warm air mass meets and pushes a cold air mass out of the way. What type of front am I?

11. I am a front that brings drizzly rain and am followed by warm clear weather. Name me.

12. A cold air mass meets a warm air but neither is very strong. They are separated and many days of wet , cloudy weather occur.

Which types of fronts can you find on this map?