Weather FrontsWeather Fronts

Air MassAir Mass•A large body of air with properties A large body of air with properties

similar to the part of Earth’s similar to the part of Earth’s surface that it covers.surface that it covers.

Air MassAir Mass• Air masses with moisture form over water Air masses with moisture form over water

and dry air masses form over land. Air and dry air masses form over land. Air masses that form at the poles are cold masses that form at the poles are cold and the ones that form in the tropics and the ones that form in the tropics (near the equator) are warm.(near the equator) are warm.

Frontal BoundariesFrontal Boundaries• Where air Where air

masses meet a masses meet a boundary, boundary, known as a known as a front, is front, is created.created.

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

Cold FrontCold Front

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

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Cold FrontCold Front• A cold air mass forces a warm air mass to rise.A cold air mass forces a warm air mass to rise.

• As the warm air rises, clouds and precipitation are As the warm air rises, clouds and precipitation are formed.formed.

• If the air is pushed upward quickly, cumulus and If the air is pushed upward quickly, cumulus and cumulonimbus clouds can form and violent storms cumulonimbus clouds can form and violent storms can result.can result.

• As the front advances, temperatures usually drop.As the front advances, temperatures usually drop.

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Warm FrontWarm Front• Shown on a weather map by a red line with Shown on a weather map by a red line with

half circles pointing in the direction that the half circles pointing in the direction that the warm air is moving.warm air is moving.

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Warm FrontWarm Front• A warm air mass catches up to and slides over aA warm air mass catches up to and slides over a

cooler air mass.cooler air mass.• Many miles ahead of the front high cirrus clouds form.Many miles ahead of the front high cirrus clouds form.• As the front approaches, steady rain or snow can occur As the front approaches, steady rain or snow can occur

over a wide area as a result of the nimbostratus and over a wide area as a result of the nimbostratus and cumulonimbus clouds that form.cumulonimbus clouds that form.

• After the front passes, wind direction changes and After the front passes, wind direction changes and temperature rises.temperature rises.

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Comparing WarmComparing Warmand Cold Frontsand Cold Fronts

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

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

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

in the air creating turbulence. in 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.

Occluded FrontsOccluded Fronts

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

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Occluded FrontsOccluded Fronts• When a slow moving warm air mass is trapped between When a slow moving warm air mass is trapped between

two fast moving cold air masses and forced to rise.two fast moving cold air masses and forced to rise.

• Stratus, nimbostratus & cumulonimbus clouds form and Stratus, nimbostratus & cumulonimbus clouds form and short steady precipitation often result.short steady precipitation often result.

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Stationary FrontsStationary Fronts• Shown on a weather map with alternating Shown on a weather map with alternating

red semicircles pointing away from the red semicircles pointing away from the warm air and blue triangles pointing away warm air and blue triangles pointing away from the cold air.from the cold air.

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Stationary FrontsStationary Fronts• A warm air mass and a cold air mass A warm air mass and a cold air mass

meet, but neither move forward.meet, but neither move forward.

• This can result in days of steady This can result in days of steady precipitation in the same area as a result precipitation in the same area as a result of nimbostratus and cumulonimbus clouds.of nimbostratus and cumulonimbus clouds.

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

Hint1

Hint2

Hint3

Hint4

Cold FrontsCold Fronts

Warm FrontsWarm Fronts

Stationary FrontsStationary Fronts

Occluded FrontsOccluded Fronts

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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Be a Weather ForecasterBe 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.

Be a Weather ForecasterBe a Weather Forecaster

• 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.

MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 2323

MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 2424

MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 2525