Air Masses &
Fronts
Chapter 17 Section 1
Pages 560-566
Air Mass
•
A huge body of air with similar
characteristics:
•
•
•
•
Humidity
Temperature
Air Pressure
Classified according to two
characteristics:
– Temperature- Where did the air mass form?
– Humidity- Did the air mass form over water
or land?
Maritime
•
Form over
oceans.
•
Water
evaporates from
the ocean
creating humid
air.
Tropical
•
Warm air masses form in the tropics
and have low air pressure.
Polar
•
•
Cold air masses form north of 50°N
latitude and south of 50°S latitude.
Have high air pressure.
Continental
•
Form over land, in the middle of
continents.
•
Very dry air.
Air Masses
Continental
Polar
Maritime
Polar
Maritime
Polar
Maritime
Tropical
Continental
Tropical
Maritime
Tropical
Maritime Tropical
• mT- originates over a warm tropical ocean.
• Warm, Moist (humid air)
• Causes high heat and humidity in the Midwest and Eastern US.
• Thunderstorms form due to the moist air
and heat available, or heavy rain or snow
in the winter.
Air Masses
Maritime Polar
• mP- Originates over the ocean.
• Cold, Damp (humid) air.
• Not as cold as cP
• If cooled to the dew point, precipitation
occurs, bring fog, rain and cool temps.
Air Masses
Continental Tropical
• cT- Originates over deserts.
• Hot and Dry air.
• Produces tremendous heat waves.
• Drought like conditions.
Air Masses
Continental Polar
• cP- Originates over Alaska and Canada.
• Cold and Dry air.
• Can create precipitation by picking up
moisture over the Great Lakes.
Air Masses
How Air Masses Move
•
The Prevailing Westerlies (a major global
wind belt) generally push air masses
from west to east in the United States.
Fronts
•
•
•
•
The area where air
masses meet and do not
mix.
Causes storms and
changeable weather.
Four types.
Determined by the
characteristics of the air
masses and how they
are moving.
Warm Fronts
•
•
•
A moving warm air mass collides with a
slower moving cold air mass.
Warm air moves over cold air. (warm air
is less dense)
Weather–
–
–
–
Clouds, storms and rain.
If humid air, light rain forms.
If dry- scattered clouds form.
After it passes, it is likely to be warm and
humid.
Warm Fronts
Cold Fronts
•
•
•
•
•
Cold air is very dense and tends to
sink.
Warm (less dense) air is pushed up.
As it rises it cools and forms clouds,
may bring heavy rain or snow.
Move very quickly, can cause abrupt
weather changes including violent Tstorms.
After it moves through, brings cool, dry
air with clear skies and cooler temps.
Cold Fronts
Stationary Fronts
•
•
•
Occurs when cold and
warm air masses meet,
but neither can force the
other to move.
Water vapor in the warm
air condenses into rain,
snow, fog or clouds.
If it stalls over an area, it
can bring these conditions
for several days.
Stationary Fronts
Occluded Fronts
•
•
•
A complex situation that occurs when a
cold front catches up with a warm front.
Pushes warm air up over colder air,
cutting the warm air off from the ground.
Weather– Ground temp= cool
– Brings rain or snowy weather.
Occluded Fronts
Surface Map
Surface Map
Surface Map
Cyclones
•
Cyclone is Greek- meaning “wheel”
•
A swirling center of low pressure.
– Spin counter-clockwise (due to coriolis effect
winds are turned to the right in the NH)
•
L is short for Low Pressure
– Air is moving towards the low
– Air is rising, forming clouds and precip.
– Bring LOUSY Weather
Anti-Cyclones
•
Are areas of high pressure centers
•
Winds spiral out from the center towards
areas of lower pressure.
– Spin clockwise (due to coriolis effect winds
are turned to the right in the NH)
•
H= short for High Pressure
– Air is moving away from the high.
– Cool air is sinking, and warms as it falls.
– Clear, dry weather. (Brings HAPPY weather)
Mid-Latitude Cyclones
Mid-Latitude Cyclones