Air masses and fronts

Air masses and fronts
• 1. An air mass is a widespread section of the
troposphere with
uniform temperature
and humidity (moisture)
• 2. The source region is
the geographic location
the air mass developed
– If air settles over one
location for a long time,
it develops the
temperature and
moisture of the area.
• Because temperature
changes so much with
latitude, tropical areas
are warm and polar are
• Oceans (maritime) carry
a lot of water vapor
• On land, (continental)
there is little water and
the air is dry.
Page 13 ESRT uses symbols for the air masses
• Dry air is small ‘cf’ or
• Moist air is small ‘m’
for maritime
• Cold air is ‘P’ for Polar
and REALLY cold air is
‘A’ for arctic.
• Warm air is ‘T’ for
And to practice:
• 1. Bringing those two
characteristics together, the air
masses may be described. For
the following, identify the
• 2. The characteristics of the air
mass is due to the
__________________ region, or
area where it formed. For each
of the following locations create
our ______ _________ (and
weather), identify the
characteristics of the air, using
the terms continental, maritime,
tropical, arctic and polar.
Gulf of Mexico:
Central Mexico:
Great Plains (winter):
Central Canada:
Northern Atlantic:
Review book Chapter 8 pages 199-200
Air masses and polar fronts: for air masses
Fronts: the boundary between two air masses
• A boundary describes
where two different
things meet.
Between countries
Between lawns
Between air and land.
A frontal boundary is where
two different air masses
meet. Energy is exchanged.
• Fronts bring a change in
• One type of air mass
pushes in and replaces
another one.
• “Bad weather” (storms
and precipitation)
occurs at fronts.
• How severe the storm is depends on:
– how quick the change is
– The differences between the 2 air masses:
• a REALLY warm, moist air mass meeting a REALLY cold, dry air mass
will produce dramatic weather/storm.
– How much moisture is in the warm air mass.
The type of front created depends on the direction the
air masses move and the way the air masses meet.
• Page 13 of ESRT lists 4
types of front and
• In the US, our weather
systems tends to move from
west to east.
• The winds in a storm, tend
to make a counterclockwise
Cold Fronts
• Side view:
Cold front overview
– Cold front, in which
heavy cold air replaces
light, warm air .
– The effect is tall,
dramatic cumulonimbus
clouds, lots of wind, and
brief and intense
precipitation. (hail, tstorms and even
• Clouds form at fronts
because warm, moist air
is pushed up at the
boundary by the heavier,
colder air mass.
• Clouds form as rising air
cools to the dew point
temperature and water
vapor condenses around
condensation nuclei,
such as soot or ash.
• Precipitation happens at
the front
Warm front: side view
Warm front: map overview
– Warm front, in which
warmer air replaces
colder air. The effect is
cirrus and stratus clouds,
steady precipitation that
may last for a day or
– Usually, the warm air
has more moisture.
– The warm air is pushed
up at the frontal
boundary, causing clouds
to form.
• The wedge-shape front
is caused by the warm
air slowly pushing up
along the boundary.
• Precipitation happens
ahead of the front.
Occluded front: side view
– Occluded front, in which a cold air mass wraps
around a warm air mass, actually lifting the air off
the ground.
– This causes a REALLY dramatic change in weather,
intense winds and violent precipitation. (Noreasters, some tornadoes and t-storms)
Stationary front
• Stationary fronts may last
for days because the 2 air
masses just don’t really
move. Usually, the
characteristics are similar to
the warm front, just
• Again, it is the warmer air that is
pushed up because it is less
• Why clouds???
• Rising air expands and
• Water vapor
Previous page: Polar front development
• Review book
chapter 8 pages
200-203 and
questions 14-21.
for fronts

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