Air Masses and Fronts

1. Air Masses and Fronts
Weather Factors

3. Properties of Air
 Air has weight  Air takes up space
 Air is all around us  Air pulls and pushes

4. Air Masses
A large body of air with similar…
Temperature
Warm
Cold
Humidity
Dry
Humid
TROPICS
POLAR
Over Water
Over Land

5. Air masses…
 Air masses DO NOT mix because of
differences in densities (warm air rises, and cold
air sinks)
 Cold air is heavy- high pressure- high density
Warm air is light- low pressure- low density

6. Air Masses’ Characteristics
Source Regions
Over warm area: the warm
area makes the air above
warm.
Over water: water
evaporates into the air
above and makes it moist.

7. Types of Air Masses
1. Maritime: (m) moist (marina/water)
2. Continental: (c) dry (continents/land)
3. Tropical: (T) warm (tropics)
4. Polar: (P) cold (poles)
DESCRIPTION CONDITION LOCATION FORMED

8. Types of Air Masses
Maritime Tropical
(mT)
Continental Tropical
(cT)
Maritime Polar
(mP)
Continental Polar
(cP)

9. FOR EACH AIR MASS – ID
1. Name of Air Mass
2. Temperature – COLD or WARM
3. Moisture - Humid or Dry
4. Origin
5. Wind – Where does it originate?

10. mP
Maritime Polar
Moist, cold air to west
coast of the US.
mT
Maritime Tropical
Moist, warm air to west
coast of the Mexico.
mT
Maritime Tropical
Moist, warm air to south
east coast of the US.Dry, warm to Desert SW
mP
Maritime Polar
Moist, cold air to east
areas of the Canada
cP
Continental Polar
Dry, cold air to central
and eastern US.
Types of Air Masses

11. Air Mass Modification
mP
Maritime Polar
Moist, cold air to west
coast of the US.
mT
Maritime Tropical
Moist, warm air to south
east coast of the US.
Air masses move by prevailing winds.
The winds cause the air masses to
move over land and water.
As the air masses move, they change.
This is called air mass modification.
The air masses becomes more like the
area it is moving over…
….. And
At the same time, the area the air mass
is moving over becomes more like the air
mass.

12. Maritime tropical air masses (mT) form over the warm waters
of the tropics and Gulf of Mexico. The northward movement
of these air masses brings warm moist air into the United States
Maritime tropical Air Mass (mT)

13. Those who live in the northern United States expect cold weather
during the winter months. These conditions usually result from the
invasion of cold arctic air masses that form from the snow covered
regions of northern Canada.

14. Notice the edge of the cold air mass is shown by the
blue line. The center of this air mass is a high
pressure center located in northern Montana
(indicated by the blue "H").

15. The leading edge of a tropical air mass surging
northward is shown by red line. Southerly winds
behind the boundary indicate the northward
movement of warm moist air.

17. Fronts
COLD FRONTS
WARM FRONTS
STATIONARY FRONTS
OCCLUDED FRONTS
A boundary between two air masses:

18. Mr. Fetch’s Earth Science Classroom
When air masses meet…
mT
Maritime Tropical
Moist, warm air to south
east coast of the US.
mP
Maritime Polar
Moist, cold air to west
coast of the US.

19. Cold air masses move southward and encounter
warm air masses. When these air masses collide,
various types of weather will result. The type of
precipitation that might result from this collision
depends on the air temperature.

20. Cold Fronts
Description:
• Cold air mass moves in to take the place of a warm air mass.
• Warm air is forced up violently.
• Steep Frontal Lifting Slope
Associated Clouds:
Cumulonimbus Clouds (Thunderstorm Clouds)
Precipitation:
• Heavy Precipitation over short periods of time due to steep frontal slope.
• Sometimes produce hail/tornadoes
Weather Map Symbol:

22. Cold Fronts

23. Cold Fronts

24. Cold Fronts

26. Warm Fronts
Description:
• Warm air mass moves in to take the place of a colder air mass.
• Warm air gently glides up over the colder air.
• Gentle Frontal Lifting Slope.
Associated Clouds:
• Nimbostratus Clouds (dark rain clouds)
Precipitation:
• Light to moderate precipitation over longer periods of time due to gentle frontal slope.
Weather Map Symbol:

29. Warm Fronts

31. The General Pattern

32. Occluded Fronts
Description:
• A cold front that catches up to a warm front by a developing cyclone.
• Warm air is forced up gently over a cooler air mass on one side.
• On the other side, the warm air is forced violently up by a colder air mass
• This cut’s off the warm are from the surface.
• A gently and steep Frontal Lifting Slope forms
Associated Clouds:
• Nimbostratus Clouds (dark rain clouds)
• Cumulonimbus Cloud s (Thunderstorm Clouds)
Precipitation:
• Light to moderate precipitation over longer periods of time due to gentle frontal slope
followed by heavy thunderstorms.
Weather Map Symbol:

34. Stationary Front
Description:
• When a warm or cold front stops moving, it becomes a
stationary front.
• Can last several days (clouds and showers)
• Once this boundary resumes its forward motion, it once
again becomes a warm or cold front.
Associated Clouds:
• Depends on the type of front:
• Warm Front - Nimbostratus
• Cold Front - Cumulonimbus
Precipitation:
• Rain and showers last several days.
Weather Map Symbol: