air masses and fronts

Air Masses and FrontsAir Masses and Fronts

ScienceScience 6 6thth Grade Grade

MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 22

Air MassAir Mass• A large body A large body

of air with of air with similar similar temperature, temperature, humidity, and humidity, and air pressureair pressure..

• Air masses Air masses form over form over large land or large land or water masses.water masses.

• Whether an air mass is warm or cold Whether an air mass is warm or cold depends on the temperature over depends on the temperature over which the mass forms.which the mass forms.

• 4 types of air masses 4 types of air masses

1.1.Tropical – warm air masses that form Tropical – warm air masses that form over the tropics.over the tropics.

2.2.Polar – cold air masses that form over Polar – cold air masses that form over the poles.the poles.

3.3.Maritime – air masses that form over Maritime – air masses that form over the ocean (very humid)the ocean (very humid)

4.4.Continental – form over land – (are Continental – form over land – (are dry)dry)MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 33

ContinentalContinental - -

• Means land. Means land.

• A Continental air A Continental air mass forms over mass forms over land.land.

Weather FrontsWeather Fronts 44

Maritime - Maritime -

• Means water.Means water.

• Maritime air Maritime air masses form masses form over water. over water.


PolarPolar

• Polar means it Polar means it forms over the forms over the poles.poles.

• COLD!COLD!


TropicalTropical

• Form over the Form over the tropics (near the tropics (near the equator)equator)

• WARM!!WARM!!



FrontsFronts• Where air masses meet but do not mix due Where air masses meet but do not mix due

to different temperatures and densities. to different temperatures and densities. becomes a front becomes a front

FrontsFronts

• 4 kinds of fronts:4 kinds of fronts:– Cold frontCold front– Warm frontWarm front– Occluded frontOccluded front– Stationary Stationary

frontfront


Cold FrontCold Front• A cold air A cold air

mass is mass is replacing a replacing a warmer air warmer air mass.mass.

• Shown on a Shown on a weather map weather map by a blue line by a blue line with triangles with triangles pointing the pointing the direction the direction the cool air is cool air is moving.moving.

Cold FrontCold Front• Rapidly moving cold air mass runs into Rapidly moving cold air mass runs into

a slowly moving warm air mass.a slowly moving warm air mass.

• The denser cold air slides under the The denser cold air slides under the lighter warm air pushing it upward.lighter warm air pushing it upward.

• The rising air cools and condenses, The rising air cools and condenses, forming clouds. forming clouds.

• Heavy rain or snow may fall.Heavy rain or snow may fall.

• If the warm air mass contains only a If the warm air mass contains only a little water vapor, there may be only little water vapor, there may be only cloudy skies. cloudy skies.


NSF North Mississippi GK-8NSF North Mississippi GK-8

Fronts: Five Types of Fronts1. Cold Front: The zone where cold air is

replacing warmer air

• Air gets drier after a cold front moves through

Cold Front Cold Front • Cold fronts move quickly and can Cold fronts move quickly and can

cause abrupt weather changes cause abrupt weather changes including violent thunderstormsincluding violent thunderstorms

• After a cold front passes through, cool, After a cold front passes through, cool, dry air moves in.dry air moves in.

• Clear skies and cooler temperatures Clear skies and cooler temperatures often follow. often follow.



Warm FrontWarm Front

• Warm air mass Warm air mass collides with a collides with a slowly moving slowly moving cooler air cooler air mass.mass.

• Shown on a Shown on a weather map weather map by a red line by a red line with half with half circles pointing circles pointing the direction the direction the warm air is the warm air is moving.moving.


• Moving warm air mass collides with a Moving warm air mass collides with a slowly moving cold air mass.slowly moving cold air mass.

• The warm air moves over the denser The warm air moves over the denser cold air. cold air.

• If the warm air is humid, showers and If the warm air is humid, showers and light rain fall along the front where the light rain fall along the front where the warm and cold air meet.warm and cold air meet.

• If the warm air is dry scattered clouds If the warm air is dry scattered clouds form. form.



Fronts: Five Types of Fronts2. Warm Front: The zone where warm

air is replacing colder air

• Air gets more humid after a warm front moves through

Warm Front Warm Front

• Because warm fronts move more Because warm fronts move more slowly than cold fronts, the weather slowly than cold fronts, the weather may be rainy or foggy for several may be rainy or foggy for several days. days.

• After the warm front passes, the After the warm front passes, the weather is likely to be warm and weather is likely to be warm and humid. humid.

• In winter, warm fronts bring snow. In winter, warm fronts bring snow.



Comparing Warm and Cold Comparing Warm and Cold FrontsFronts

• Cold fronts move faster than warm fronts. Cold fronts move faster than warm fronts.

• The weather activity in a cold front is often The weather activity in a cold front is often violent and happens directly at the front.violent and happens directly at the front.

• Cold fronts have sudden gusty winds high in Cold fronts have sudden gusty winds high in

the air creating turbulence. the air creating turbulence.

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

• In a warm front the cloud formation is very In a warm front the cloud formation is very low often creating situations of poor visibility.low often creating situations of poor visibility.


Occluded FrontsOccluded Fronts• When a warm When a warm

front is trapped front is trapped by 2 cold fronts.by 2 cold fronts.

• Shown on a Shown on a weather map weather map by a purple line by a purple line with alternating with alternating triangles and triangles and semicircles semicircles pointing the pointing the direction the direction the front is moving.front is moving.

Occluded FrontsOccluded Fronts• A warm air mass is caught between A warm air mass is caught between

two cooler air masses. two cooler air masses.

• The denser cool air masses move The denser cool air masses move underneath the less dense warm air underneath the less dense warm air and push it upward.and push it upward.

• The temperature near the ground The temperature near the ground becomes cooler. becomes cooler.


Occluded FrontsOccluded Fronts


• The warm air mass is cut off, or The warm air mass is cut off, or occluded, from the ground. occluded, from the ground.

• As the warm air cools and its water As the warm air cools and its water vapor condenses, the weather may vapor condenses, the weather may turn cloudy and rainy or snowy. turn cloudy and rainy or snowy.


Fronts: Five Types of Fronts4. Occluded Front: Formed when a cold

front overtakes a warm front

• This occurrence usually results in storms over an area

• In U.S., the colder air usually lies to the west

MAP TAP 2002-2003MAP TAP 2002-2003

Stationary FrontsStationary Fronts• A front that stops moving or is moving very A front that stops moving or is moving very

slowly.slowly.

• Shown on a weather map with alternating red Shown on a weather map with alternating red semicircles pointing away from the warm air and semicircles pointing away from the warm air and blue triangles pointing away from the cold air.blue triangles pointing away from the cold air.

http://www.windows.ucar.edu/earth/Atmosphere/images/stationary_front_sm.jpg

Stationary Fronts Stationary Fronts • Sometime cold and warm air masses Sometime cold and warm air masses

meet, but neither has enough force to meet, but neither has enough force to move the other.move the other.

• They meet in a “standoff”They meet in a “standoff”


Stationary FrontsStationary Fronts

• Where the warm and cool air meet, Where the warm and cool air meet, water vapor in the air condenses into water vapor in the air condenses into rain, snow, fog, or clouds. rain, snow, fog, or clouds.

• It may stall over an area and bring It may stall over an area and bring many days of clouds and many days of clouds and precipitation.precipitation.



Fronts: Five Types of Fronts3. Stationary Front: When either a cold

or warm front stops moving

• When the front starts moving again it returns to either being a

cold or warm front

Locate the 4 types of fronts on Locate the 4 types of fronts on this weather map.this weather map.

Cold FrontsCold Fronts

Stationary FrontStationary Front

Occluded FrontOccluded Front

Weather FrontsWeather Fronts 3333

Be a Weather ForecasterBe 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.

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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.



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

air masses and fronts

Documents

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colder air air

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cold fronts

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