Air Masses and FrontsWeather Patterns

What is an Air Mass?

• An AIR MASS is a large body of air that takes on the TEMPERATURE and HUMIDITY (moisture) of a region

• Usually THOUSANDS of miles in diameter

• Forms over a source region with relatively stable conditions

• Named for the SOURCE REGION (where it comes from)

Two Air Masses: each air mass has roughly the same temperature and humidity

Types of Air Masses: Named by where they come from!

• POLAR: source region (colder air mass) (P)

• TROPICAL: source region (warmer air mass) (T)

(basically north or south) **************************************

• MARITIME: Source region (formed over the ocean)(m)

• CONTINENTAL: Source region (formed over land) (c)

(over ocean or land)

Types of Air Masses:

Maritime Tropical (mT): form over the tropical oceans, very humidMaritime Polar (mP): form over cold ocean areas, cool but humid air

Continental Tropical (cT): Hot, dry , air masses from the southwest Continental polar (cP): cool or cold dry air

Can you find the different continental air masses?

These circles enclose air masses. What is the name of a line that surrounds an area of EQUAL TEMPERATURE? ISOTHERM

QUESTION:WHICH AIR MASS DO YOU THINK WOULD PRESS DOWN ON THE EARTH MORE?

a COLD AIR MASS or a WARM Air MASS?

WHY?

How do the air masses move?

• WINDS! • Uneven heating of the earth’s

surface causes convection currents which cause differences in pressure, which causes winds.

• Prevailing westerlies generally push the air masses from WEST EAST

FRONTS

Where Air Masses collide

What is a FRONT?• A weather FRONT forms when two

unlike air masses meet (cold and warm air masses)

• Because of the difference in TEMPERATURE and DENSITY of the air masses, the meeting results in storms and changing weather.

• Fronts are named by which air mass is MOVING!

FOUR FRONTS

• COLD FRONT- cold air mass moving

• WARM FRONT- warm air mass moving

• STATIONARY FRONT – neither air mass moving

• OCCLUDED FRONT-warm air mass caught between two cold air masses

Colder, more

dense air.

Warmer, less dense air.

IF AIR MASS #1 MOVES TOWARDS AIR MASS #2 COLD FRONT

COLD FRONT SYMBOL:

COLD FRONT

Colder, more

dense air.

Warmer, less dense air.

•Cold Air moves in quickly to replace warmer air

•Warmer air will rise, cool, then form large, CUMULONIMBUS CLOUDS (the thunderstorm kind) •Usually cause short lived, violent STORMS (rain, snowfall)

COLDFRONT

COLD FRONT DIAGRAM:

What happens to the temperature after a cold front moves though an area?

WARM FRONT

IF AIR MASS #2 MOVES TOWARDS AIR MASS #1 WARM FRONT

WARM FRONT SYMBOL:

Air Mass #1Colder, More Dense Air

Air Mass #2Warmer, Less dense Air

WARM FRONT

•Warm Air Mass moves in to replace colder air mass•Moves SLOWER than Cold front•Clouds that form are thinner (not puffy)•Usually causes LIGHTER, but LONGER periods of precipitation•In winter, brings snow.

Air Mass #1Colder, More Dense Air

Air Mass #2Warmer, Less dense Air

WARM FRONT DIAGRAM:

WARM AIR MASS collides with a cold air mass. Warm air slowly moves OVER cold air. Longer rain storms.

STATIONARY FRONT

A COLD AIR MASS AND A WARM AIR MASS MEET, BUT NEITHER HAS THE FORCE TO MOVE THE OTHERWARM FRONT SYMBOL:

Cold Air Mass

Warm Air Mass

Cold fronts move FASTER than warm fronts.

The weather activity in a cold front is often VIOLENT and happens directly at the front. Cold fronts have sudden gusty winds high in the air creating turbulence.

The weather activity in a warm front generally happens before the front passes.

Comparing Warm and Cold Fronts

SO WHY DO WE NEED TO KNOW ABOUT FRONTS????

BECAUSE FRONTS ARE WHERE THE STORMS ARE!!!!!!

HURRICANE

Locate the 4 types of fronts on this weather map.

Hint1

Hint2

Hint3

Hint4

Cold Fronts

Warm Front

Stationary Front

Occluded Front

Weather Fronts 34

Be a Weather Forecaster

You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F.

You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F.

Use the map to help you predict whether the temperature in Alabama will increase, decrease, or stay the same. Explain why you think so.

35

Be a Weather Forecaster

There is a cold front approaching. The temperatures will probably be cooler behind the front.

There is a cold front approaching. The temperatures will probably be cooler behind the front.

Weather Fronts 36MAP TAP 2002-2003

Be a Weather Forecaster

• Of course, meteorologists (weather forecasters) use much more data than fronts and air masses to help them forecast the weather more accurately. But any forecast is just a prediction of what might happen. Even with the best data, weather forecasts can be wrong.