Lesson 2-2Lesson 2-2Weather ElementsWeather Elements

Part 1 of 2Part 1 of 2

Chapter 2, Lesson 2

Lesson OverviewLesson Overview

Types of air masses and fronts Factors that impact air masses FrontsFronts Wind and Atmospheric Motion High- and low-pressure systems Terrain factors that affect weatherTerrain factors that affect weather Normal weather patterns in U.S.Normal weather patterns in U.S.

Types of Air Masses and FrontsTypes of Air Masses and Fronts

Weather refers to temperature, moisture, wind Weather refers to temperature, moisture, wind velocity, visibility, and barometric pressurevelocity, visibility, and barometric pressure

Air massAir mass Large body of air (usually 1,000+ miles acrossLarge body of air (usually 1,000+ miles across Generally same temperature and moisture content Generally same temperature and moisture content

within the entire masswithin the entire mass

Chapter 2, Lesson 2Chapter 2, Lesson 2 Courtesy of NASA

Fronts are the boundary Fronts are the boundary between two different air between two different air massesmasses

Air MassesAir Masses Air masses are classified based on their source regionAir masses are classified based on their source region

Polar air mass (P) is coldPolar air mass (P) is cold Tropical air mass (T) is warmTropical air mass (T) is warm Maritime air mass (m) forms over water and is humidMaritime air mass (m) forms over water and is humid Continental air mass (c) forms over land and is dryContinental air mass (c) forms over land and is dry

Possible Types:Possible Types: mPmP mTmT cPcP cTcT AA

Air Mass ClassificationAir Mass Classification

Air Mass ClassificationAir Mass Classification

Aviators and meteorologists in the U.S. are Aviators and meteorologists in the U.S. are mainly concerned with air masses originating mainly concerned with air masses originating from two sourcesfrom two sources• Masses that move south and east from Polar RegionsMasses that move south and east from Polar Regions• Masses that move north and east from Tropical Masses that move north and east from Tropical

Regions (mainly the Gulf of Mexico)Regions (mainly the Gulf of Mexico)

Temperature ClassificationTemperature Classificationof Air Massesof Air Masses

Based upon its temperature in relation to Based upon its temperature in relation to the surface over which it passesthe surface over which it passes A cold air mass is cooler than the Earth’s A cold air mass is cooler than the Earth’s

surface over which it is movingsurface over which it is moving Tends to create updrafts with this air massTends to create updrafts with this air mass

A warm air mass is warmer than the Earth’s A warm air mass is warmer than the Earth’s surface over which it is movingsurface over which it is moving Typically won’t exhibit updraftsTypically won’t exhibit updrafts

Air Mass CharacteristicsAir Mass Characteristics

Outside factors affecting air mass characteristics include:Outside factors affecting air mass characteristics include: Source RegionSource Region Surface qualities of terrain air mass passes over Surface qualities of terrain air mass passes over The seasons (fall, winter, spring, summer)The seasons (fall, winter, spring, summer)

As an air mass moves away from its source, its temp and As an air mass moves away from its source, its temp and pressure traits change due to the surface it passes over. pressure traits change due to the surface it passes over. Can become warmer or colderCan become warmer or colder Can absorb or lose moistureCan absorb or lose moisture Can be lifted up by mountains or subside into valleysCan be lifted up by mountains or subside into valleys

Cold air masses move quicker than warm air massesCold air masses move quicker than warm air masses Weather generally depends on the nature of a prevailing Weather generally depends on the nature of a prevailing

air mass or the interaction of two or more air massesair mass or the interaction of two or more air masses

Air Masses -- Quick ReviewAir Masses -- Quick Review

Where do air masses originate?Where do air masses originate? In a source regionIn a source region

How do they form? How do they “adopt” the How do they form? How do they “adopt” the temperature and moisture traits of their source temperature and moisture traits of their source region?region? By remaining over an area long enoughBy remaining over an area long enough

What type of terrain makes an ideal source region?What type of terrain makes an ideal source region?

Flat, uniform areas where temperature and Flat, uniform areas where temperature and moisture don’t change rapidlymoisture don’t change rapidly

Air Masses -- Quick ReviewAir Masses -- Quick Review

What traits can change?What traits can change? Can become warmer or colderCan become warmer or colder Can become wetter or drierCan become wetter or drier

As an air mass moves away from its source, what As an air mass moves away from its source, what causes its traits to change?causes its traits to change?

The surface the air mass passes overThe surface the air mass passes over

What is the letter designation for a moist polar air What is the letter designation for a moist polar air mass?mass? mPmP

Air Masses -- Quick ReviewAir Masses -- Quick Review

How do you define a cold air mass?How do you define a cold air mass? An air mass that is cooler than the surface it An air mass that is cooler than the surface it

passes overpasses over

What is the process called when an air mass drifts What is the process called when an air mass drifts away from its source region and adopts the temp and away from its source region and adopts the temp and moisture trais of the surface over which it passes?moisture trais of the surface over which it passes? ModificationModification

What happens when two different air masses meet?What happens when two different air masses meet? Fronts develop and weather changesFronts develop and weather changes

FrontsFronts

Fronts are the boundaries between two different air massesFronts are the boundaries between two different air masses They always signal a change in weatherThey always signal a change in weather As fronts move along the surface, one air mass is displacing the As fronts move along the surface, one air mass is displacing the

other air massother air mass

Chapter 2, Lesson 2 Reproduced from NASA

Four types based on temperature of Four types based on temperature of advancing air compared with advancing air compared with temperature of the air it is replacingtemperature of the air it is replacing Cold Front => cold air mass replaces Cold Front => cold air mass replaces

warmer air warmer air massmass

Warm Front => warm air mass Warm Front => warm air mass replaces replaces

colder air colder air mass mass

Types of FrontsTypes of Fronts

WarmWarm ColdCold StationaryStationary OccludedOccluded

Chapter 2, Lesson 2 Courtesy of NASA

Warm FrontWarm Front Usually connected to a low-pressure cell Usually connected to a low-pressure cell Usually moves slowly in east-northeast directionUsually moves slowly in east-northeast direction If warm air mass did not move, the front would dissipateIf warm air mass did not move, the front would dissipate The warm front slips upward over cool air and forms a wedgeThe warm front slips upward over cool air and forms a wedge Rises slowly which delays condensationRises slowly which delays condensation

Warm FrontWarm Front As warm front advances, it replaces colder air As warm front advances, it replaces colder air Before a warm front arrives, you’ll likely see:Before a warm front arrives, you’ll likely see:

High-level cirrus clouds, layered stratus clouds, and fogHigh-level cirrus clouds, layered stratus clouds, and fog As the front passes over you’ll see:As the front passes over you’ll see:

Stratus clouds and some drizzle and fogStratus clouds and some drizzle and fog After it passes, you’ll see:After it passes, you’ll see:

Stratocumulus and nimbostratus clouds and rain showers Stratocumulus and nimbostratus clouds and rain showers

Warm FrontWarm Front Question: Why is fog so common in warm fronts as they pass Question: Why is fog so common in warm fronts as they pass

over and past your location?over and past your location? After front passes, there is a rise in temperatures, general After front passes, there is a rise in temperatures, general

clearing and change in wind directionclearing and change in wind direction In winter a warm front causes icing conditions at low altitudesIn winter a warm front causes icing conditions at low altitudes In northern latitudes snow may also be producedIn northern latitudes snow may also be produced

Cold FrontCold Front Cold fronts generally move from northwest to southeast.Cold fronts generally move from northwest to southeast. Can travel very far southCan travel very far south Amount of energy depends on amount of cold air and how Amount of energy depends on amount of cold air and how

high the pressure ishigh the pressure is As the cold air mass catches up to the warmer air mass, cold As the cold air mass catches up to the warmer air mass, cold

air forces the warm air upward air forces the warm air upward

Cold FrontCold Front As cold air pushes the warm air upwards, the cold air replaces As cold air pushes the warm air upwards, the cold air replaces

the warm air near the surfacethe warm air near the surface Before the cold front arrives, you’ll see:Before the cold front arrives, you’ll see:

Cirrus, cirrocumulus, cirrostratus; clouds get lower as front gets closerCirrus, cirrocumulus, cirrostratus; clouds get lower as front gets closer As the front passes over:As the front passes over:

Cumulus or cumulonimbus clouds form => rain, hail, wind, etcCumulus or cumulonimbus clouds form => rain, hail, wind, etc After the front passes:After the front passes:

Clouds dissipate, clear skies, cooler weatherClouds dissipate, clear skies, cooler weather

Cold FrontCold Front

In western states:In western states: The most noticeable change is shift of wind, temperature, and blowing dustThe most noticeable change is shift of wind, temperature, and blowing dust

In southern and eastern states:In southern and eastern states: Generally lots more moisture, larger areas of cloud development, and Generally lots more moisture, larger areas of cloud development, and

more problems for aviatorsmore problems for aviators

Test Question: Why are there more cumulonimbus build-ups and Test Question: Why are there more cumulonimbus build-ups and tornado activity associated with cold fronts than warm fronts?tornado activity associated with cold fronts than warm fronts?

Cold FrontCold Front

Along the cold front there will be a Along the cold front there will be a low-pressure cell where weather is low-pressure cell where weather is worstworst

Almost any type of clouds can be Almost any type of clouds can be found near the cellfound near the cell Squall lines are common ahead of these fast Squall lines are common ahead of these fast

moving frontsmoving fronts Poor visibility, low ceilings and rain in summerPoor visibility, low ceilings and rain in summer Freezing rain and snow in winterFreezing rain and snow in winter

Stationary FrontStationary Front Forms between two air masses of relatively equal Forms between two air masses of relatively equal

strengthstrength When air masses stop, a stationary front developsWhen air masses stop, a stationary front develops

Weather can be bad for aviation along the frontWeather can be bad for aviation along the front About every form of weather can be foundAbout every form of weather can be found

Stationary FrontStationary Front

Toward the trailing edge of the any front there will be Toward the trailing edge of the any front there will be a stationary-front conditiona stationary-front condition

The trailing edge stationary fronts are a great distance The trailing edge stationary fronts are a great distance from the parent cellfrom the parent cell

As the distance become greater the front no longer As the distance become greater the front no longer exists.exists.

Occluded FrontOccluded Front Forms when fast–moving cold front catches up Forms when fast–moving cold front catches up

with slow–moving warm frontwith slow–moving warm front There is a tendency for a horizontal bend or wave There is a tendency for a horizontal bend or wave

to occur along the frontto occur along the front After a frontal bend starts, cold air moves ahead After a frontal bend starts, cold air moves ahead

of a warm frontof a warm front

Occluded FrontOccluded Front Warm Front Occlusion:Warm Front Occlusion:

Air mass overtaking the warm front is not as cool as the Air mass overtaking the warm front is not as cool as the cold air in front of the warm front, and rides over the cold cold air in front of the warm front, and rides over the cold air mass while lifting the warm airair mass while lifting the warm air

Cold Front Occlusion:Cold Front Occlusion: Air mass overtaking the warm front is cooler than the cool Air mass overtaking the warm front is cooler than the cool

air ahead of the warm front, and plows under both air air ahead of the warm front, and plows under both air massesmasses

Occluded FrontOccluded Front

A wide variety of weather can be found along A wide variety of weather can be found along an occluded frontan occluded front

Thunderstorms possible, but usually their Thunderstorms possible, but usually their passage is associated with a drying of the air passage is associated with a drying of the air mass mass

Next….Next….

Types of air masses and fronts Factors that impact air masses FrontsFronts High- and low-pressure systems Terrain factors that affect weatherTerrain factors that affect weather

Chapter 2, Lesson 2