Download Air Masses and Fronts

What are Air Masses and Fronts?
(Chapter 16 Section 2)
Terms: air mass, front, cyclone,
anticyclone,
What are air masses and fronts?
P. 490
 What are the major air
masses that influence
the weather in the
U.S.?
 What is one source
region of a maritime
polar air mass?
 What are the
characteristics of an
air mass whose twoletter symbol is cP?
 What are the four
major types of fronts?
Air Masses
 Air masses are large bodies of air
where temperature and moisture
content are constant throughout.
 Moisture content and temperature of
a mass are determined by the area
over which the air mass forms.
 These areas are called source
regions.
Types of Air Masses
 maritime (m) – forms over water;
wet
 Continental (c) – forms over land; dry
 Polar (P) – forms over the polar
regions; cold
 Tropical (T) – develops over the
tropics; warm
Cold Air Masses
 Three polar air masses:
 Continental polar (cP) forms over northern
Canada; brings extremely cold weather during
winter; brings cool dry weather during summer
 Maritime polar (mP) forms over North Pacific
Ocean; cool, very wet; rain and snow during
winter; foggy during summer
 Maritime polar (mP) forms over North Atlantic
Ocean; cool, cloudy and precipitation during
winter; mild, cloudy during summer.
Warm Air Masses
 There are three warm air masses that
affect the U.S.
 Maritime tropical (mT) forms over warm water in
the Pacific ocean
 (mT) forms over the Gulf of Mexico and the
Atlantic Ocean; brings hot, humid weather and
hurricanes and thunderstorms during the
summer; In winter, brings mild, cloudy weather
 Continental Tropical (cT) forms deserts of Mexico
and Southwestern U.S.; brings clear, hot, dry
weather during summer
Fronts
 The boundary between air masses of
different densities and different
temperatures
 Cold Front – cold air moves under warm
air; brings thunderstorms
 Warm Front – warm air moves over cold
air; brings drizzly rain followed by clear
and warm weather.
Fronts
 Occluded Front – warm air mass is caught
between two colder air masses. Brings cool
temperature and large amounts of rain.
 Stationary Front – cold air mass meets
warm air mass; remain separate; not
enough energy to move warm air above
cold air mass; can bring many days of
cloudy, wet weather.
Air Pressure and Weather
 Cyclones – areas in the atmosphere
that has lower pressure than the
surrounding areas and has winds that
spiral toward the center. Brings
clouds and rain.
 Anticyclones – the rotation of air
around a high pressure center in the
direction opposite to Earth’s rotation.
Brings dry, clear weather.
Quick Check
 What kind of front forms when a cold
air mass displaces a warm air mass?
A. a cold front
B. a warm front
C. an occluded front
D. a stationary front
Quick Check
 A maritime tropical air mass contains
A. cold, dry air.
B. warm, dry air.
C. warm, wet air.
D. cold, wet air.
Quick Check
 A front that forms when a warm air
mass is trapped between two cold air
masses and is forced to rise is a(n)
A. stationary front.
B. occluded front.
C. warm front.
D. cold front.