Transcript Air Masses and Fronts

Air Masses and Fronts
An air mass is a large volume of air in the troposphere with
similar characteristics of temperature, pressure and moisture as
the portion of the Earth’s surface it formed over.
T = Tropical air masses form in
warm areas.
P = Polar air masses
form in cool areas
c = Continental air masses are
formed over the land. These
air masses tend to be dry.
Air masses tend to
be represented by
symbols on a map
A = Arctic air masses form in
very cold areas
m = Maritime air masses are
formed over the water. These
air masses tend to be moist.
The various
symbols for air
masses are found
on pg. 13 of RT
Air Masses of North America
Maritime
Polar
(cool and
moist)
mP
Maritime
Tropical
(warm and
moist)
mT
Continental
Polar
(cool and
dry)
cP
Continental
Tropical
(warm and
dry)
cT
Continental
Arctic
(very cool
and dry)
cA
Maritime
Tropical
(warm and
moist)
mT
High and Low Pressure Systems
In the Northern Hemisphere,
low pressure systems spin
counterclockwise. Winds
blow towards the low
pressure center
(convergence).
In the Northern Hemisphere,
high pressure systems spin
clockwise. Winds blow away
from the high pressure
center (divergence).
Fronts
A front is the interface between air masses.
Severe weather conditions are often
associated with fronts.
RT = Pg.
13
There are four different
fronts that represent the
areas where air masses
meet.
Each front is represented
by a unique set of
symbols and colors.
Cold Front
In a cold front, an advancing cold air mass pushes against a warm air mass.
The warm air mass is less dense and rises above the cold air mass. The rising
air forms large cloud systems associated with severe storms (thundershowers).
Rain is usually associated in regions just ahead of, on top of, and behind
the cold front.
Warm Front
In a warm front, an advancing warm air mass meets a cold air mass moving in
the same direction.
The warm air mass is less dense and rises above the cold air mass. The warm
air moves on top of the cold air (like a wedge). A layer of different types of
clouds arranged throughout the atmosphere is seen in a warm front. .
Rain is usually associated in regions just ahead of the warm front.
Stationary Front
In a stationary front, an advancing warm air mass meets an advancing cold air
mass moving in opposite directions.
The warm air mass is less dense than the cold air mass and rises at the
boundary of the front. Sometimes it may take weather patterns a longer time to
move across a region due to the opposing movement of the air masses.
Cloudy skies and/or rain is usually associated in regions at the stationary
front.
Occluded Front
In a occluded front, an advancing cold air mass overtakes a warm air mass to
meet up with another cold air mass. The warm air is forced above both cold air
masses and is responsible for cloud development associated with precipitation.
Occluded fronts are associated with the formation of cyclones (low pressure
systems).
Very low air pressure and stormy conditions are associated in regions at
the occluded front.