Download Chapter 3 Notes

Weather Changes as Air Masses
Move
Chapter 3 section 1 Notes
Air masses are large bodies of air.
•An air mass is a large volume
of air in which the temperature
and humidity are nearly the
same throughout.
•An air mass can cover many
thousands of square kilometers.
•The air gradually takes on the
characteristics of the land or
water below it.
What air masses bring as they move
•As an air mass moves, it
brings its temperature and
moisture to new locations.
•When an air mass moves to a
new region, it carries along its
characteristic moisture and
temperature.
How Weather Systems move from Place
to Place (Air Masses Video)
http://player.discoveryeducation.com/index.cfm?guid
AssetId=5CDF74DF-97DC-4BA1-996AC13E68455E0E&blnFromSearch=1&productcode=
US (c. 3:54 Min.)
Weather changes where air masses
meet.
•Warm and cold air masses
don’t mix together, they
stay separate from each
other
•A front is a boundary
between air masses.
•The weather near a front
can differ from the weather
inside the rest of an air
mass.
Fronts and Weather
•Different types of fronts produce
different patterns of weather.
•When a cold, dense air mass pushes
warmer air, it produces a cold front.
•When a warm air mass pushes colder
air, it produces a warm front.
A Cold front Photo
Cold Fronts
•Cold fronts can move into a
region quickly.
•Cold fronts often produce
tall cumulonimbus clouds
and precipitation. Brief
heavy storms are likely.
•Strong thunderstorms can
develop and form tornadoes.
Cold Fronts & Weather
•After the storms, the air is
cooler and often very clear.
•Triangles show the
direction that a cold front
moves.
Draw a cold front symbol
here!
Warm Fronts
•Warm fronts move more slowly
than cold fronts.
•Warm air moves gradually up
and over a mass of denser and
colder air.
•Moisture in the warm air
condenses all along the sloping
front, producing cloud-covered
skies.
A warm front approaches
•As a warm front
approaches, you may
first see high cirrus
clouds, then high stratus
clouds, then lower and
lower stratus clouds.
Cloud progression of a warm front
2
1
3
4
Warm Fronts & Weather
•Often, a warm front brings
many hours of steady rain or
snow.
•After the front passes, the
air is usually warmer.
•Semicircles show the
direction that a warm front
moves.
•Draw a warm front symbol
here!
Stationary Fronts
•Stationary fronts occur when air
masses first meet or when a cold
or warm front stops moving.
•For a while, the boundary
between the air masses stays in the
same location – it stays stationary.
•The air along the front can still
move sideways or upward.
Stationary Fronts Continued
•The upward air motion may
produce clouds that cover the sky,
sometimes for days at a time. (This
can produce severe flooding.)
•When the front starts moving, it
becomes a warm front if the warm
air advances and pushes the cold
air.
•Alternating triangles and
semicircles show a stationary front.
•Draw a stationary front symbol
here!
Weather Fronts Video
http://player.discoveryeducation.com/index.
cfm?guidAssetId=5CDF74DF-97DC-4BA1996AC13E68455E0E&blnFromSearch=1&produ
ctcode=US (C. 3:03 Min.)
High and Low Pressure Systems
•H = center of High
Pressure System
•L = center of a Low
pressure system.
High Pressure Systems
•At a high-pressure
center, air sinks slowly
down. As the air nears
the ground, it spreads
out toward areas of
lower pressure.
•In the Northern
Hemisphere, the Coriolis
effect makes the air turn
clockwise as it moves
outward.
•http://www.bom.gov.au/lam/Stu
dents_Teachers/pressure.shtml
High Pressure Systems Continued
•A high-pressure system
is formed when air moves
all the way around a
high-pressure center.
•A high-pressure system
generally brings clear
skies and calm air or
gentle breezes.
Low-pressure Systems
•A low-pressure system is a
large weather system that
surrounds a center of low
pressure.
•It begins as air moves
around and inward toward
the lowest pressure and then
up to higher altitudes.
•The rising air produces
stormy weather.
Low-pressure Systems Continued
•The rising air produces
stormy weather.
•In the Northern Hemisphere,
the air in a low-pressure
system circles in a
counterclockwise direction.
Cold Fronts go with High-pressure
Systems & Thunderstorms
This video shows a thunderstorm formed along a cold
front (Thunderstorms 7:30 Min)
http://player.discoveryeducation.com/index.cfm?guidAssetId=
3CE03830-3031-4DFC-928B84E8B80CBDC7&blnFromSearch=1&productcode=US
Rain
Shower
Warm fronts go with Low-pressure
Systems
Blizzard
Tropical Storm
Hurricane Andrew
Weather Changes as Air Masses
Move
Knowing how to identify different types of
fronts, low and high pressure systems, and
the weather associated with them, will help
you prepare for whatever weather lies
ahead.