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Weather
Temperature
You will usually see temperature measured in °F
for maps of the United States
Maps of foreign countries will usually be
measured in °C
Temperature
Instrument used to measure temperature is a
thermometer.
Relative Humidity
The relative humidity tells us how “full” the air is
with water at the time of measurement.
For example, 90% relative humidity means that
at that moment the air is holding 90% of the
maximum amount of water it could.
Relative Humidity
Instrument used to measure relative humidity
is a psychrometer.
Cloud Cover Symbols
You will often see
the circles drawn on
a weather map
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
High and Low Pressure Cells
anticyclone
cyclone
D O C
High Pressure Cell
heavenly
I C U
moves toward a
cool
dry
Low Pressure Cell
warm
lousy
wet
Air Pressure
Instrument used to measure air pressure is a
barometer.
Air Masses
Air Masses
Fronts
A front is the boundary separating air masses of
different densities
Fronts extend both vertically and horizontally
in the atmosphere
Fronts: Four Types of Fronts
1. Cold Front: The zone where cold air is
replacing warmer air
In U.S., cold fronts usually move from
northwest to southeast
Air gets drier after a cold front moves
through
Fronts: Four Types of Fronts
2. Warm Front: The zone where warm air is
replacing colder air
In U.S., warm fronts usually move from
southwest to northeast
Air gets more humid after a warm front
moves through
Fronts: Four Types of Fronts
3. Stationary Front: When either a cold or
warm front stops moving
When the front starts moving again it
returns to either being a cold or warm
front
Fronts: Four Types of Fronts
4. Occluded Front: Formed when a cold
front overtakes a warm front
This occurrence usually results in storms
over an area
In U.S., the colder air usually lies to the
west
Fronts
Name
Date
Types of Weather Fronts
STUDENT RESOURCE 8.4
INFORMATION SHEET
When large masses of warm air and cold air meet, they do not
mix. Instead, they form a front, usually hundreds of miles long.
When a front passes, the weather changes. The chart describes
the four main types of fronts and the weather changes each
type brings.
Type of Front
Cold front
Cold air
How It Forms
Forms when a cold air
mass pushes under a warm
air mass, forcing the warm
air to rise.
Warm air
Front moving this way
Warm front
Warm air
Copyright © Houghton Mifflin Company. All Rights Reserved.
Cold air
Front moving this way
Stationary front
Cold air
Warm air
Little or no forward
movement of the front
Occluded Front
Warm air
Cold air
Cold air
Front moving this way
Weather It Brings
Thunderheads can form as
the moisture in the warm
air mass rises, cools, and
condenses. As the front
moves through, cool, fair
weather is likely to follow.
Forms when a moist, warm As the warm air mass rises,
air mass slides up and over it condenses into a broad
a cold air mass.
area of clouds. A warm
front brings gentle rain
or light snow, followed by
warmer, milder weather.
Forms when warm and
cold air meet and neither
air mass has the force
to move the other. They
remain stationary, or
“standing still.”
Where the warm and cold
air meet, clouds and fog
form, and it may rain or
snow. Can bring many
days of clouds and precipitation.
Forms when a warm air
mass gets caught between
two cold air masses. The
warm air mass rises as the
cool air masses push and
meet in the middle.
The temperature drops
as the warm air mass is
occluded, or “cut off,”
from the ground and
pushed upward. Can bring
strong winds and heavy
precipitation.
WEATHER AND WATER • SECTION 8 AIR MASSES AND FRONTS
Clouds: Five Types of Clouds
1. High-Level Clouds: Usually found at greater
than 20,000 ft.
Usually made of ice crystals
Examples include Cirrus, Cirrostratus
Clouds: Five Types of Clouds
2. Mid-Level Clouds:
Usually found between
6,500 and 20,000 ft.
Usually made of water droplets, but can be
made of ice
Example is altocumulus
Clouds: Five Types of Clouds
3. Low-Level Clouds: Usually found lower than
6,500 ft.
Low, lumpy clouds that produce weak to
moderate precipitation
Examples include Nimbostratus and
Stratocumulus
Clouds: Five Types of Clouds
4. Vertically developed: These clouds are thick
and puffy and extend very far upwards
Examples include Cumulonimbus and Fair
Weather Cumulus
Ordinary Cumulus clouds can quickly become
Cumulonimbus clouds that start strong
thunderstorms
Clouds: Five Types of Clouds
5. Other: These are miscellaneous clouds
These clouds do not really fit into any category,
and all have different characteristics
Examples include billow clouds, contrails,
mammatus, orographic, and pileus
Weather Maps: Pressure &
Temperature
Weather Maps: Doppler Radar
Maps
Summary
Temperature: Usually in °F, need to convert to °C
High pressure areas cause sunny weather; low
pressure areas cause rain and storms
Five Types of air masses:
1. Continental Polar
2. Continental Tropical
3. Maritime Polar
4. Maritime Tropical
5. Continental Arctic
Summary (continued)
Four types of fronts:
1. Cold
2. Warm
3. Stationary
4. Occluded
Five types of clouds:
1. High Level
2. Mid Level
3. Low Level
4. Vertically developed
5. Miscellaneous
Sources
Palmer, Chad and Evans, David. May 20, 2005. Occluded fronts can
signal weakening of storm. Accessed 28 October 2005. http://
www.usatoday.com/weather/tg/wofront/wofront.htm
Palmer, Chad and Kepple, Kevin. May 20, 2005. High-pressure systems
brings sunny days. Accessed 27 October 2005.
http://www.usatoday.com/weather/tg/whighp/whighp.htm
Palmer, Chad and Kepple, Kevin. May 20, 2005. How low pressure
systems affect weather. Accessed 27 October 2005. http://
www.usatoday.com/weather/tg/wlowpres/wlowpres.htm
Weather World 2010, University of Illinois. No date of publication
given. Reading and Interpreting Weather Maps. Accessed 21 October
2005. http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml