Lesson 2-2
Weather Elements
Part 1 of 2
Lesson Overview
 Types
of air masses and fronts
 Factors that impact air masses
 Fronts
 Wind and Atmospheric Motion
 High- and low-pressure systems
 Terrain factors that affect weather
 Normal weather patterns in U.S.
Chapter 2, Lesson 2
Types of Air Masses and Fronts
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Weather refers to temperature, moisture, wind
velocity, visibility, and barometric pressure
Air mass
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Large body of air (usually 1,000+ miles across
Generally same temperature and moisture content
within the entire mass
Fronts are the boundary
between two different air
masses
Chapter 2, Lesson 2
Courtesy of NASA
Air Masses

Air masses are classified based on their source region
Polar air mass (P) is cold
 Tropical air mass (T) is warm
 Maritime air mass (m) forms over water and is humid
 Continental air mass (c) forms over land and is dry
Possible Types:
 mP
mT
 cP
cT
 A
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Air Mass Classification
Air Mass Classification

Aviators and meteorologists in the U.S. are
mainly concerned with air masses originating
from two sources
•
•
Masses that move south and east from Polar Regions
Masses that move north and east from Tropical
Regions (mainly the Gulf of Mexico)
Temperature Classification
of Air Masses

Based upon its temperature in relation to
the surface over which it passes
A cold air mass is cooler than the Earth’s
surface over which it is moving
 Tends to create updrafts with this air mass
 A warm air mass is warmer than the Earth’s
surface over which it is moving
 Typically won’t exhibit updrafts

Air Mass Characteristics
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Outside factors affecting air mass characteristics include:
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As an air mass moves away from its source, its temp and
pressure traits change due to the surface it passes over.
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Source Region
Surface qualities of terrain air mass passes over
The seasons (fall, winter, spring, summer)
Can become warmer or colder
Can absorb or lose moisture
Can be lifted up by mountains or subside into valleys
Cold air masses move quicker than warm air masses
Weather generally depends on the nature of a prevailing
air mass or the interaction of two or more air masses
Air Masses -- Quick Review

Where do air masses originate?
 In a source region

How do they form? How do they “adopt” the
temperature and moisture traits of their source
region?
 By remaining over an area long enough

What type of terrain makes an ideal source region?

Flat, uniform areas where temperature and
moisture don’t change rapidly
Air Masses -- Quick Review

What is the letter designation for a moist polar air
mass?
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As an air mass moves away from its source, what
causes its traits to change?


mP
The surface the air mass passes over
What traits can change?


Can become warmer or colder
Can become wetter or drier
Air Masses -- Quick Review

What is the process called when an air mass drifts
away from its source region and adopts the temp and
moisture trais of the surface over which it passes?
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How do you define a cold air mass?
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
Modification
An air mass that is cooler than the surface it
passes over
What happens when two different air masses meet?

Fronts develop and weather changes
Fronts
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Fronts are the boundaries between two different air masses
They always signal a change in weather
As fronts move along the surface, one air mass is displacing the
other air mass
Four types based on temperature of
advancing air compared with
temperature of the air it is replacing
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
Cold Front => cold air mass replaces
warmer air mass
Warm Front => warm air mass
replaces colder air
mass
Chapter 2, Lesson 2
Reproduced from NASA
Types of Fronts
Warm
 Cold
 Stationary
 Occluded

Chapter 2, Lesson 2
Courtesy of NASA
Warm Front
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Usually connected to a low-pressure cell
Usually moves slowly in east-northeast direction
If warm air mass did not move, the front would dissipate
The warm front slips upward over cool air and forms a wedge
Rises slowly which delays condensation
Warm Front
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As warm front advances, it replaces colder air
Before a warm front arrives, you’ll likely see:
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As the front passes over you’ll see:
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High-level cirrus clouds, layered stratus clouds, and fog
Stratus clouds and some drizzle and fog
After it passes, you’ll see:

Stratocumulus and nimbostratus clouds and rain showers
Warm Front
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Question: Why is fog so common in warm fronts as they pass
over and past your location?
After front passes, there is a rise in temperatures, general
clearing and change in wind direction
In winter a warm front causes icing conditions at low altitudes
In northern latitudes snow may also be produced
Cold Front
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Cold fronts generally move from northwest to southeast.
Can travel very far south
Amount of energy depends on amount of cold air and how
high the pressure is
As the cold air mass catches up to the warmer air mass, cold
air forces the warm air upward
Cold Front
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As cold air pushes the warm air upwards, the cold air replaces
the warm air near the surface
Before the cold front arrives, you’ll see:
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As the front passes over:
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Cirrus, cirrocumulus, cirrostratus; clouds get lower as front gets closer
Cumulus or cumulonimbus clouds form => rain, hail, wind, etc
After the front passes:
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Clouds dissipate, clear skies, cooler weather
Cold Front
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In western states:
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In southern and eastern states:
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The most noticeable change is shift of wind, temperature,
and blowing dust
Generally lots more moisture, larger areas of cloud
development, and more problems for aviators
Test Question: Why are there more cumulonimbus
build-ups and tornado activity associated with cold
fronts than warm fronts?
Cold Front

Along the cold front there
will be a low-pressure cell
where weather is worst

Almost any type of clouds
can be found near the cell
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Squall lines are common ahead of
these fast moving fronts
Poor visibility, low ceilings and
rain in summer
Freezing rain and snow in winter
Stationary Front
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Forms between two air masses of relatively equal
strength
 When air masses stop, a stationary front develops
Weather can be bad for aviation along the front
About every form of weather can be found
Stationary Front
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Toward the trailing edge of the any front there will be
a stationary-front condition
The trailing edge stationary fronts are a great
distance from the parent cell
As the distance become greater the front no longer
exists.
Occluded Front
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Forms when fast–moving cold front catches up
with slow–moving warm front
There is a tendency for a horizontal bend or wave
to occur along the front
After a frontal bend starts, cold air moves ahead
of a warm front
Occluded Front

Warm Front Occlusion:
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
Air mass overtaking the warm front is not as cool as the
cold air in front of the warm front, and rides over the cold
air mass while lifting the warm air
Cold Front Occlusion:

Air mass overtaking the warm front is cooler than the
cool air ahead of the warm front, and plows under both
air masses
Occluded Front
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A wide variety of weather can be found along
an occluded front
Thunderstorms possible, but usually their
passage is associated with a drying of the air
mass
Next….
 Types
of air masses and fronts
 Factors that impact air masses
 Fronts
 High- and low-pressure systems
 Terrain factors that affect weather
Chapter 2, Lesson 2