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Lesson 3: North America WeatherSystems
Pages 206-207
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Dominant factors that produce seasonal weather
Temperature Wind Pressure Moisture
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Define Weather System
Weather system is a set of temperature, wind, pressure, and moisture conditions for a certain region that moves as a unit for a period of days.
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Define Air Mass
Air mass is a large body of air in which the temperature and moisture content at a specific altitude are fairly uniform.
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Types of Air Masses
1. Maritime
2. Continental
3. Polar
4. Tropical
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Air Masses: Maritime
Maritime means it is formed over water
It forms over the Atlantic or Pacific Oceans
It soaks up water from the ocean The air will be wet
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Air Masses: Continental
Continental means it formed over the land
Very little moisture over landAir will be dry
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Air Masses: Polar
Polar means it formed over the cold regions of the North Pole
Covered in ice and snowAir over this area is cold
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Air Masses: Tropical
Tropical means the air mass is formed in the warm tropical regions
Air mass gains a lot of energy from the sun
Air over this region is warm
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Air Masses
Polar (cold) Tropical (Warm)
Maritime (wet)
Wet and cold Wet and warm
Continental (Dry)
Dry and cold Dry and warm
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Types of Air Masses
1. Maritime Polar
2. Continental Polar
3. Maritime Tropical
4. Continental Tropical
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Maritime Polar
Polar maritime air masses are cold and wet and usually bring fog and cool temperatures in the summer and heavy snow and very cold temperatures in the winter.
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Continental Polar
Continental Polar air masses form over northern Canada and bring cold, dry air in the winter.
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Maritime Tropical
Maritime Tropical air masses are warm and wet and usually bring warm "muggy" rain in the summer and slushy snow and mild temperatures in the winter.
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Continental Tropical
Continental Tropical air masses form over Mexico and bring dry and hot air in the summer.
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Define Front
When two air masses meet the boundary that forms between them is called a front. The weather conditions at the front is usually very stormy and unsettled. Fronts mean rain!
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Four Types of Fronts
1. Warm Fronts
2. Cold Fronts
3. Occluded Fronts
4. Stationary Fronts
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Warm Fronts
A warm front is caused by a warm air mass moving slowly up a stationary (stopped) cold air mass. As the warm air slowly rises and cool showers (or flurries) develop. Conditions are somewhat calm. The air that follows behind the warm front is warm and humid (damp).
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Cold Fronts
Cold air mass pushes underneath a warm air mass. The warm air is forced up. As the warm air rises it
begins to cool and loses its moisture. Forms clouds at first but then develops into heavy
rain (or snow) and stormy weather. The air that follows behind the cold front is cool and dry.
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Occluded Fronts
An occluded front is formed when a cold air mass catches up with a slower moving warm air mass. The cold air mass slowly pushes the warm air up creating gentle precipitation. Storms caused by an occluded front are generally gentle.
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Stationary Fronts
Stationary fronts form when two air masses collide and stall (stop).
The front slowly moves through over a long period of time. Stationary fronts usually bring rain / or snow for long periods of time and the conditions stay quite calm. It is common to have rain, drizzle and fog lasting for days!
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