Airmasses and Fronts

What are air masses?

● Large Bodies of
air.
● Form when the
air over a large
region sits in one
place for many
days.

What are the two characteristics that
describe air masses?

Moisture
Temperature

How do differentiate Air masses in

terms of Moisture?

● Continental air masses-designated by the

lowercase

letter

"c",

originate

over

continents and are therefore dry air
masses.

● Maritime air masses-designated by the

letter "m", originate over the oceans and are
therefore moist air masses.

How do differentiate Air masses in

terms of Temperature?

● Tropical

o Air masses formed near the equator
o WARM AIR

● Polar
● o Air masses formed closer to the poles

o COLD AIR

Air Masses

• Large bodies of air with constant

temperature & moisture (USA has 4)
– cP (continental polar) : cold, dry stable air
– cT (continental tropical) : hot, dry, stable air
– mP (maritime polar) : cool, moist, unstable

air

– mT (maritime tropical) : warm, moist,

unstable air

High Pressure Areas (H)

• When cool air sinks & is

warmed, the air can
hold more moisture.

• Often associated with

sunny skies

• Winds move clockwise

Low Pressure Areas (L)

• When warm air rises

and is cooled, the air
can not hold as much
moisture

• Often associated with

precipitation and
stormy weather

• Winds move counter

clockwise

So, if you see…

• So if you see a big H: expect happy (fair)

weather

• So if you see a big L: expect lousy (stormy)

weather

Air Mass Movement

• Air masses move

based on a
difference in
pressure.

• They move from

High to Low
pressure areas.

• Weather in the US

moves from West to
East

Warm Front

• A warm front is warm air replacing cool air
• Warm air must “overrun” cold air
• These are usually slow moving

Cold Fronts

• Cold air advances into region of warm air
• Short, intense storms
• Clearing conditions after front passes

Stationary Front

• Surface positions of the front do not move
• Often a region of clouds

Occluded Front

• Cold front overtakes a warm front
• Often found close to the low pressure center