low pressure systems vs high pressure systems. let’s compare low pressure systems (l) high...

Low Pressure Systems vs

High Pressure Systems

Let’s Compare

Low Pressure Systems (L)

High Pressure Systems (H)

Look!!! Convecting air…

LOW PRESSURE SYSTEMSLow pressure systems involve air that tends to rise, thus causing clouds and precipitation. Those near the equator tend to be high energy due to strong ground heating (convectional). Low pressure systems may develop tornadoes and sometimes develop into hurricanes, fuelled by warm, very humid air evaporated from tropical oceans in summer. They tend to be fast moving, with plenty of cloud cover that reduces temperature range, strong winds and high rainfall.

LOW PRESSURE SYSTEMS

Hurricane off USA fueled by hot humid air over the Caribbean


A convectional cumulonimbus cloud results from strong ground heating at

the equator


A tornado may develop from a cumulonimbus cloud

HIGH PRESSURE

High Pressure means that air tends to sink. Sinking air is compressed, warms up as a result and its relative humidity falls below saturation. Any clouds evaporate. Rainfall is unlikely.

CLEAR SKIES CAUSE FROST

HIGH PRESSURE

� High pressure systems have clear skies, varying winds, little rainfall.� Visibility is typically good�Cloud cover is slight, resulting in a high ranges of temperature (hot days, cold nights).

FEW CLOUDS

VISIBLITY REMAINS BETTER IN MOUNTAINS - LESS POLLUTION

CLEAR SKIES

LITTLE WIND

Weather FrontsWeather FrontsTeacherPage

MAP TAP 2002-2003MAP TAP 2002-2003 Weather FrontsWeather Fronts 1111

Air MassAir Mass• A large body A large body

of air with of air with similar similar temperature temperature and moisture.and moisture.

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


Frontal BoundariesFrontal Boundaries• Where air masses Where air masses

interact – also interact – also know as a front.know as a front.

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

Cold FrontCold Front• A cold air mass A cold air mass

is replacing a is 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.

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Cold FrontCold Front• Thunderheads Thunderheads

can form as can form as the moisture the moisture in the warm in the warm air mass rises, air mass rises, cools, and cools, and condenses. condenses. As the front As the front moves moves through, cool, through, cool, fair weather is fair weather is likely to likely to follow.follow.

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Warm FrontWarm Front• Warm air mass Warm air mass

replacing a replacing a 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.

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Warm FrontWarm Front• As the warm air As the warm air

mass rises, it mass rises, it condenses into condenses into a broad area of a broad area of clouds. A clouds. A warm front warm front brings gentle brings gentle rain or light rain or light snow, followed snow, followed by warmer, by warmer, milder weather.milder weather.

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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 (after the front has passed).(after the front has passed).

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

the air creating turbulence. the air creating turbulence.

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

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Occluded FrontsOccluded Fronts• The The

temperature temperature drops as the drops as the warm air mass warm air mass is is occludedoccluded, or , or “blocked,” from “blocked,” from the ground and the ground and pushed upward. pushed upward. Can bring Can bring strong winds strong winds and heavy and heavy precipitation.precipitation.

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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.

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MAP TAP 2002-2003MAP TAP 2002-2003

Stationary FrontsStationary Fronts• Where the warm and cold air meet, clouds Where the warm and cold air meet, clouds

and fog form, and it may rain or snow. and fog form, and it may rain or snow. Can bring Can bring many hours or days of clouds many hours or days of clouds and precipitation.and precipitation.

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

Hint1

Hint2

Hint3

Hint4

Cold FrontsCold Fronts

Warm FrontWarm Front

Stationary FrontStationary Front

Occluded FrontOccluded Front

Weather FrontsWeather Fronts 2727

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.

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

2828

Be a Weather ForecasterBe a Weather Forecaster

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.


SummarySummary• Describe the Describe the 4 types4 types of fronts of fronts andand

the the weatherweather associated with each associated with each front.front.

low pressure systems vs high pressure systems. let’s compare low pressure systems (l) high...

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