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- Air Masses and Fronts
Types of Air Masses
 Air masses are large bodies of air that has
properties similar to the part of the Earth
over which it developed.
 Air masses can be warm or cold, and humid
or dry. As an air mass moves into an area,
the weather changes.
- Air Masses and Fronts
Classifying Air Masses
 Four major types
of air masses
influence the
weather in North
America: maritime
tropical,
continental
tropical, maritime
polar, and
continental polar.
North American Air Masses
High and Low Pressure Areas
• High pressure
causes air to sink
• Usually results in
several days of clear
sunny skies
• Air rises in low
pressure areas and
forms water
droplets
• Usually results in
rain and storms
How a Front Forms
 Any Boundary between two different air
masses
 Generally means a change in weather
 Four Types
Types of Fronts
Cold Front
Occurs when colder air advances toward warm
air. Cold air wedges under warmer air.
Warm Front
 Forms when lighter, warmer air advances
over heavier, colder air.
Stationary Front
 Occurs when a boundary between air
masses stops advancing.
Occluded Front
 Forms when a cold air mass moves toward a cool
air with warm air between the two. The colder air
forces the warm air upward.
- Air Masses and Fronts
Comparing and Contrasting
 compare and contrast the four types of fronts
by completing a table like the one below.
Front
How It Forms
Cold front
A cold air mass
overtakes a warm air
mass.
A warm air mass
overtakes a cold air
mass.
Cold and warm air
masses meet, but neither
can move the other.
A warm air mass is caught
between two cold air
masses.
Warm front
Stationary front
Occluded front
Types of
Weather
Clouds, possibly storms
with heavy precipitation
Clouds, light
precipitation
Clouds, precipitation
Clouds, precipitation
- Storms
Thunderstorm Formation
 A thunderstorm forms when warm, humid air
rises rapidly within a cumulonimbus cloud.
- Storms
Tornado Formation
 Tornadoes can form when warm, humid air
rises rapidly in thick cumulonimbus clouds—
the same type of clouds that bring
thunderstorms.
- Storms
Tornado Alley
 Tornadoes in the U.S. are most likely to
occur in a region known as Tornado Alley.
- Storms
Structure of a Hurricane
 In a hurricane, air moves rapidly around a
low-pressure area called the eye.
- Storms
Hurricane Andrew
 The path of Hurricane Andrew over three
consecutive days can be seen below.
Severe Weather
Type of Storm
Where Forms
Hurricane
Safety Rules
Spring or
Summer
Seek shelter,
avoid trees and
water.
Cumulonimbus
cloud
Spring, early
summer
Move to a storm
shelter or basement
if possible; stay away
from windows and
doors.
Over warm
ocean water
Late summer
and into
autumn
Evacuate or
move inside a
well-built building.
Within large
Thunderstorms cumulonimbus
clouds
Tornado
Typical Time of
Year
- Predicting the Weather
Reading Weather Maps
 Weather maps in newspapers use symbols to
show fronts, high- and low-pressure areas, and
precipitation. Color bands indicate different
temperature ranges.
- Predicting the Weather
Reading Weather Maps
 This is the type of weather map produced by
the National Weather Service. It shows data
collected from many weather stations.
Isobars
 Isobars- connect areas of equal
barometric pressure
 Isotherm- connects areas of
equal temperature
Isobars
Weather Maps: Pressure &
Temperature
- Predicting the Weather
Reading Weather Map Symbols
 The figure below shows what various
weather symbols mean in a station model.
Cloud Cover Symbols
• You will often see
the circles drawn on
a weather map
Weather Maps: Doppler Radar
Maps
Where are the Fronts?
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Where are the Fronts?
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