Chapter 29

Air Masses and FrontsAir Masses and Fronts

BFRB Pages 123- 125BFRB Pages 123- 125

Air MassesAir 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 MassesTYPES of Air Masses• maritime Tropical (maritime Tropical (mTmT)- warm & humid air)- warm & humid air• continental Tropical (continental Tropical (cTcT)- hot (warm) & dry )- hot (warm) & dry

airair• maritime Polar (mP)- cold & humid airmaritime Polar (mP)- cold & humid air• continental Polar (continental Polar (cPcP)- cold & dry air)- cold & dry air• continental Arctic (continental Arctic (cAcA)- very cold & dry air )- very cold & dry air • THESE ARE ALL LISTED IN THE ESRT’s THESE ARE ALL LISTED IN THE ESRT’s

ON PAGE 13 ON THE BOTTOM!ON PAGE 13 ON THE BOTTOM!

• There are no mA air masses – WHY???There are no mA air masses – WHY???

FrontsFronts • boundaryboundary between two air masses between two air masses

• bring changes in the weather (from bring changes in the weather (from west to east)west to east)

• VIF!!!!VIF!!!! - Fronts are named for the air - Fronts are named for the air that is that is behindbehind them them

• The 4 types of fronts and their The 4 types of fronts and their symbols are listed in the ESRT’s on symbols are listed in the ESRT’s on Page 13 on the bottomPage 13 on the bottom

COLD AIR MASSCOLD AIR MASS

WARM AIR MASSWARM AIR MASS

Air Mass Army AnalogyAir Mass Army Analogy

• Think of air masses as an army front (the Think of air masses as an army front (the army is army is BEHINDBEHIND the frontline) the frontline)

• At the Front there is FIGHTING and lots of At the Front there is FIGHTING and lots of VIOLENCE (VIOLENCE (stormy weatherstormy weather))

• Behind the front (Behind the front (inside the air massinside the air mass) the ) the general sits on his duff and watches the general sits on his duff and watches the goings-on while enjoying the goings-on while enjoying the nice weathernice weather!!

FIGHTING - STORMSFIGHTING - STORMS

NICE WEATHERNICE WEATHER

Cold FrontCold Front • Cold Cold densedense air pushes warm air pushes warm less denseless dense air air

up and out of the wayup and out of the way• Cold fronts usually move very quickly and Cold fronts usually move very quickly and

bring bring short periods of showers/thunderstormsshort periods of showers/thunderstorms• Lower temperatures are behind the front Lower temperatures are behind the front • SYMBOL – the direction of the “arrows” SYMBOL – the direction of the “arrows”

points towards the direction the front is points towards the direction the front is MOVINGMOVING

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 FrontWarm Front • Warm air moves up and over the cold front Warm air moves up and over the cold front

as it as it slowly displacesslowly displaces the cold air the cold air• Warm fronts move slowly, and bring Warm fronts move slowly, and bring many many

days of steady precipitationdays of steady precipitation• Higher temperatures are behind the frontHigher temperatures are behind the front• SYMBOL – direction of “semi-circles” is SYMBOL – direction of “semi-circles” is

the direction the front is movingthe 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 FrontStationary Front • The air from the warm front and cold The air from the warm front and cold

front meet, but front meet, but do not movedo not move

• These fronts have similar weather These fronts have similar weather conditions as warm fronts conditions as warm fronts

• SYMBOL – warm and cold fronts SYMBOL – warm and cold fronts are moving in opposite directions, are moving in opposite directions, thus making a stationary conditionthus making a stationary condition

Cross Section View – look at the spread out, horizontal stratus clouds

Occluded FrontOccluded Front • Cold air catches up to and Cold air catches up to and overtakesovertakes a a

warm front (often warm front (often squeezing it between squeezing it between another cold frontanother cold front))

• May produce precipitation for many days May produce precipitation for many days

• SYMBOL – cold and warm fronts “mix” SYMBOL – cold and warm fronts “mix” hence the purple color - the “bumps” are hence the purple color - the “bumps” are also on the SAME SIDE OF THE LINE also on the SAME SIDE OF THE LINE (sometimes just a mix of red & blue (sometimes just a mix of red & blue symbols)symbols)

Overhead View On Map

Cross Sectional View

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 SNOWLAKE EFFECT SNOW• Great Lakes Region – NYSGreat Lakes Region – NYS• cP air mass passes over the cP air mass passes over the

warmer & more humid lake air warmer & more humid lake air causing it to rise rapidly and form causing it to rise rapidly and form into cumulonimbus cloudsinto cumulonimbus clouds

• HEAVY snowfall occurs rapidlyHEAVY snowfall occurs rapidly• Western NYS is known as the Western NYS is known as the

SNOW CAPITAL of the USA!SNOW CAPITAL of the USA!