Fronts and Fronts and Pressure SystemsPressure Systems

ReviewReview

What is an air mass?What is an air mass?

a large volume of air in which a large volume of air in which temperature and humidity are nearly temperature and humidity are nearly the same in different locations over a the same in different locations over a large area .large area .

What happens when What happens when air masses meet?air masses meet?

Weather can change.Weather can change.

New air moving into an area brings New air moving into an area brings different weather.different weather.

FrontsFronts

A A frontfront is a boundary between two air is a boundary between two air masses.masses.

As one air mass pushes another, warm As one air mass pushes another, warm air at the boundary will be pushed air at the boundary will be pushed upwards.upwards.

This forms clouds.This forms clouds.

So it forms clouds…So it forms clouds…

Often weather will become cloudy or Often weather will become cloudy or stormy when a front passes.stormy when a front passes.

Once the front has passed you will Once the front has passed you will experience the temperature and experience the temperature and humidity of the new air mass.humidity of the new air mass.

How do I know which one How do I know which one it is?it is?

The names tell you which way the The names tell you which way the temperature will change and which temperature will change and which type of front it is.type of front it is.

Colder air comes with a cold front.Colder air comes with a cold front.

Warmer air comes with a warm front.Warmer air comes with a warm front.

Cold FrontsCold Fronts

When cold air moves into an area of When cold air moves into an area of warmer air you have a cold front.warmer air you have a cold front.

Move quickly.Move quickly.

Has a steep front edge.Has a steep front edge.

Warm air rises steeply and quickly. Warm air rises steeply and quickly. Forms Cumulonimbus CloudsForms Cumulonimbus Clouds

Cold FrontCold Front

Rising AirRising Air

Quickly rising warm air cools and Quickly rising warm air cools and water vapor condenses on water vapor condenses on condensation nuclei producing tall condensation nuclei producing tall cumulonimbus clouds and usually cumulonimbus clouds and usually precipitation.precipitation.

After the storm the air is usually After the storm the air is usually cooler and very clear.cooler and very clear.

ExampleExample

What would the weather be like if a What would the weather be like if a cold front moved into Muncy today?cold front moved into Muncy today?

And on a weather map…And on a weather map…

The blue triangles represent a cold front.

ReviewReview

Explain a cold front.Explain a cold front.How air rises?How air rises?What cloud type forms?What cloud type forms?What type of weather follows?What type of weather follows?

What do we use to show a cold What do we use to show a cold front on a map?front on a map?

Warm FrontsWarm Fronts When warm air moves into an area of When warm air moves into an area of

cooler air you have a warm front.cooler air you have a warm front.

Moves slowly.Moves slowly.

Air rises slowly.Air rises slowly.

Warm air moves up and over the Warm air moves up and over the mass of colder air.mass of colder air.

CloudsClouds Warm air rises slowly and water Warm air rises slowly and water

vapor condenses forming clouds.vapor condenses forming clouds. There are a series of cloud types There are a series of cloud types

as warm fronts approach.as warm fronts approach.11stst – cirrus – cirrus22ndnd – altocumulus or altostratus – altocumulus or altostratus33rdrd – stratus / nimbostratus – stratus / nimbostratus

Brings hours of steady rain or Brings hours of steady rain or snow.snow.

Warm FrontWarm Front

On a weather map…On a weather map…

Red semicircles represent a warm front.

ReviewReview

High and Low PressureHigh and Low Pressure

Cyclone – location with the lowest pressure

Anticyclone – location with highest pressure

PressurePressureHigh pressure rotates clockwise and outward as air moves to areas of low pressure.

Low preesure rotates counterclockwise and inward then lifts upward.

                                                                                  

Low Pressure System 

                                                                

High Pressure System

On a weather map…On a weather map…

ActivityActivity

When you are done with the power When you are done with the power point notes open the following link point notes open the following link and complete and complete “Precipitation Along “Precipitation Along Fronts” Fronts” scaffolding activity.scaffolding activity.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/fpr.rxml

Activity 2Activity 2

When you are done with the power When you are done with the power point notes open the following link point notes open the following link and complete and complete “Pressure” “Pressure” scaffolding activity and complete all scaffolding activity and complete all work 1-5.work 1-5.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/prs.rxml

Activity 3Activity 3

When you are done with the power When you are done with the power point notes open the following link point notes open the following link and complete and complete “Midlatitude “Midlatitude Cyclone” Cyclone” scaffolding activity and scaffolding activity and complete questions 1-5.complete questions 1-5.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/cyc.rxml