Air Masses & Fronts – Notes
What Is An Air Mass?
• An AIRMASS is a large body of air in the lower troposphere that has similar characteristics
throughout.
• An air mass can be several thousand kilometers in diameter and several kilometers high.
• The TEMPERATURE and HUMIDITY are nearly uniform throughout.
• The temperature and humidity depend on where the air mass originates.
Where Do Air Masses Originate?
• Air masses originate in Source Regions.
• Air masses do not move far from their source.
• Air masses are classified by TEMPERATURE and HUMIDITY.
Tropical = Warm
Polar = Cold
Arctic = Very Cold
Maritime = Wet
Continental = Dry
Air Mass Classification
Where Air
Mass Forms
Area of
Country
Impacted
Air Mass
Symbol
Temperature
and Humidity
Maritime
Tropical
mT
Warm & Wet
Low latitudes
over water
Southwest and
Southeast U.S.
Maritime Polar
mP
Cold & Wet
High latitudes
over water
Northeast and
Northwest U.S.
Continental
Polar
cP
Cold & Dry
High latitudes
over land
Midwest to
Eastern U.S.
Continental
Tropical
cT
Warm & Dry
low latitudes
over land
Southwest U.S.
Continental
Arctic
cA
Very Cold &
very Dry
High latitudes
over land
Northern U.S.
in winter
Air Mass Names/Source Regions
As an air mass moves, its characteristics change and so does the weather for the area over
which it moves.
For example - if a warm/moist air mass moves over an area, that place will experience warmer
temperatures and higher humidity.
The Air Mass itself will eventually cool down and become drier. (It takes on characteristics of
the area it moved over.)
NOTES – WEATHER PATTERNS AND FRONTS
Weather patterns are caused by the movement of air masses and what happens when
different ______________________.

_______________ – boundary between two air masses.

Air masses meet but rarely mix.
Cold Front: boundary along an advancing cold air
mass that is replacing & moving under a warmer air
mass.
 Rising warm air usually produces cumulonimbus
clouds and thunderstorms.
 Air becomes cooler after front passes. Air pressure
increases and skies clear.
Warm Front: boundary where an advancing warm
air mass is replacing & rising over a cooler air mass.
 1st cirrus clouds appear days in advance, then
rain arrives ahead of front.
 Air becomes warmer and skies clear after the
front passes.
Occluded Front: boundary where a cold air
mass pushes a warm air mass up and over
another cold air mass.
 Most complex since it involves 3 air masses.
Warm
 when a cold front ‘catches up’ to a warm
front, producing clouds & precipitation
Stationary front: A boundary where a cold and
a warm air mass meet but neither are strong
enough to replace each other.
Warm
 when a front stops moving forward, producing
clouds & precipitation
– causes floods if stationary too long.
Fronts and Weather Patterns- Notes
Name
COLD FRONT
WARM
FRONT
STATIONARY
FRONT
OCCLUDED
FRONT
Formation
Clouds
Weather
Symbol
-Strong Winds
-Heavy rain
-Altocumulus
-Thunderstorms
-Cumulonimbus
-Lightning
-Tornados
-Cirrus
-Cirrostratus
-Altostratus
-Nimbostratus
-Cirrus clouds then
rain showers arriving
ahead of the front
-Cirrus
-Cirrostratus
-Altostratus
-Nimbostratus
-Unchanging weather
-Typically steady rain
for days along the
front
-Flooding can occur if
still for too long
-Cumulus
-Strong winds and
-Cumulonimbus heavy rain
WHY ARE FRONTS ASSOCIATED WITH LOW PRESSURE? Cold air masses/fronts usually mover faster because they are more dense.
FRONT MOVEMENT: Most weather moves from west to east across the United States. All Fronts move forward accept for stationary.