Chapter 20 Reading Guide
Weather
20.1 Air Masses and Weather
What is an air mass and how does it typically gain its specific characteristics?
An air mass is a large body of air with similar characteristics throughout. It gains these
characteristics from the air temperature and humidity in its place of origin. As it moves,
it takes these characteristics with it, but may also change in response to new
surroundings.
Record the characteristics of the five main types of air masses.
Place of Origin
Continental Arctic
(cA)
Maritime Polar
(mP)
Artic, Polar Regions
Continental Polar
(cP)
Inland Alaska and
Canada
High latitude oceans
Continental Tropical Southern deserts
(cT)
Maritime Tropical
Warm tropical
(mT)
oceans
Direction of
Movement
Southerly
Southerly and
toward the U.S.
center
Southeasterly
Northerly
Northerly and
toward the U.S.
center
Weather Impact
Extreme cold, little
precipitation
Fog, clouds,
precipitation
Cold, little
precipitation except
Lake Effect snow
Heat waves, drought
Heat, humidity,
thunderstorms
20.2 Fronts and Lows
1. Define and explain the stage at which a low-pressure system produces the most intense
storm.
A low-pressure system creates the most intense storm after about 12-24 hours, when its
warm front becomes occluded between cool air pushing northward in front of it and cold
air pushing southward behind it.
Complete the organizer with information describing different fronts and the weather they
bring.
1. Warm Front
2. Cold Front
Forms when warm air advances on cooler
air; gradual slope as warm air rises slowly
moves slowly; large areas of precipitation,
lasting several days.
Forms when cold air advances on warmer
air; steep slope as cold air sinks quickly
moves quickly, any precipitation is brief;
brings thunderstorms or cool breezes,
depending on humidity in displaced warm
air.
4. Stationary Front
3. Occluded Front
Front forms when warm front is trapped
between two cold fronts often causes
cloudiness, precipitation.
Forms when front doesn’t move; warmer
air rises within the front, causing
precipitation; heavy storms due to
stationary precipitation.
20.3: Thunderstorms and Tornadoes
Complete the organizer by listing the conditions and locations where thunderstorms most
often develop, then listing and defining their possible effects.
THUNDERSTORMS DEVELOP

1. a.) in moist stable air
b.) in warming temps of
afternoon
c.) at frontal boundaries or
when warm air hits other
obstacles

and can cause

2.
Lightning

which is

\
4. Tornadoes

which are

3. an electrical discharge when positive and 5. Violently rotating columns of
negative charges in a thundercloud collide
air that touch the ground.
and form a spark
List and describe some ways that meteorologists predict tornadoes and warn people of the
related danger.
Meteorologists use conventional radar to map precipitation in an area and Doppler radar
to identify the wind directions within a storm. Doppler radar can identify the
mesocyclone wind movements often associated with tornadoes. Tornado watches and
warnings advise people of the possible tornado danger at any given time.
20.4: Hurricanes and Winter Storms
Complete the organizer to help you track the steps in the formation, development, impact,
and weakening of a hurricane.
1.
Mild atmospheric disturbance over tropical
ocean

2. Humid Air
Rises
8. storm
weakens over
cooler land or
water


7. Storm nears land
causing:
a.) storm surge
b.) damaging
winds
c.) heavy rain
d.) inland flooding
e.) heavy surf
3.Air cools and
condenses
releasing heat


6. Storm moves
according to global
wind patterns
4. Cycle of air
movement
continues

\
5. Coriolis effect
rotates air in the
storm.
List and describe the characteristics of a blizzard: A blizzard is a special kind of midlatitude low-pressure system. It has winds over 56 km/hour, temperatures below -7C,
and falling or blowing snow that reduces visibility.
20.5: Forecasting Weather
In the organizer below, record important elements of the forecasting process.
1. Satellites take
visible and infrared
pictures
\
2. Radiosondes
measure temperature,
humidity, pressure

/
4. Station models
+
5. surface
weather map
3.surface
observations
measure
temperatures,dew
point, barometric
pressure, wind
speed and
direction
=
6. knowledge of local
weather patterns
7. forecasts
Explain why it is important that weather station models and surface maps be readable to
meteorologists in any country:
In this way, meteorologists around the world can share data, and forecast farther ahead
and provide necessary warnings of bad weather.