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Chapter 29
Air Masses and Fronts
BFRB Pages 123- 125
Air Masses
• Large areas (blobs) of the
troposphere that have approximately
the same weather, temperatures and
humidity
• Air Mass Types - Named for where
they develop over and come FROM
• Weather changes occur with changes
in air masses
TYPES of Air Masses
• maritime Tropical (mT)- warm & humid air
• continental Tropical (cT)- hot (warm) & dry
air
• maritime Polar (mP)- cold & humid air
• continental Polar (cP)- cold & dry air
• continental Arctic (cA)- very cold & dry air
• THESE ARE ALL LISTED IN THE ESRT’s
ON PAGE 13 ON THE BOTTOM!
• There are no mA air masses – WHY???
Fronts
• boundary between two air masses
• bring changes in the weather (from
west to east)
• VIF!!!! - Fronts are named for the air
that is behind them
• The 4 types of fronts and their
symbols are listed in the ESRT’s on
Page 13 on the bottom
WARM AIR MASS
COLD AIR MASS
Air Mass Army Analogy
• Think of air masses as an army front (the
army is BEHIND the frontline)
• At the Front there is FIGHTING and lots of
VIOLENCE (stormy weather)
• Behind the front (inside the air mass) the
general sits on his duff and watches the
goings-on while enjoying the nice weather!
NICE WEATHER
FIGHTING - STORMS
Cold Front
•
•
•
•
Cold dense air pushes warm less dense
air up and out of the way
Cold fronts usually move very quickly
and bring short periods of
showers/thunderstorms
Lower temperatures are behind the front
SYMBOL – the direction of the “arrows”
points towards the direction the front is
MOVING
Cross Sectional View
Overhead View on Map
Cross Section View – Why does the cold air
mass stay near the ground and lift the warm air
mass up?
Warm Front
•
•
•
•
Warm air moves up and over the cold
front as it slowly displaces the cold air
Warm fronts move slowly, and bring
many days of steady precipitation
Higher temperatures are behind the
front
SYMBOL – direction of “semi-circles” is
the direction the front is moving
Cross Sectional View
Overhead View on Map
Cross Section View – Why does the
warm air mass slowly override the
cold mass cause long periods of rain?
Stationary Front
• The air from the warm front and cold
front meet, but do not move
• These fronts have similar weather
conditions as warm fronts
• SYMBOL – warm and cold fronts are
moving in opposite directions, thus
making a stationary condition
Cross Section View – look at the
spread out, horizontal stratus clouds
Occluded Front
•
•
•
Cold air catches up to and overtakes a
warm front (often squeezing it between
another cold front)
May produce precipitation for many days
SYMBOL – cold and warm fronts “mix”
hence the purple color - the “bumps” are
also on the SAME SIDE OF THE LINE
(sometimes just a mix of red & blue
symbols)
Cross Sectional View
Overhead View On Map
This is the jet stream. It moves from West to East
in the US and dictates what our weather will be.
What kind of air is being brought to NY right now?
LAKE EFFECT SNOW
• Great Lakes Region – NYS
• cP air mass passes over the
warmer & more humid lake air
causing it to rise rapidly and form
into cumulonimbus clouds
• HEAVY snowfall occurs rapidly
• Western NYS is known as the
SNOW CAPITAL of the USA!