What Causes the What Causes the Weather?Weather?

Air MassesAir Masses

Air MassesAir Masses

► Large Bodies of air (Can be 1000s of sq Large Bodies of air (Can be 1000s of sq miles)miles)

► Form over both land and waterForm over both land and water►Over Land Air Masses are:Over Land Air Masses are:

DryDry Warm in summer and cold in winterWarm in summer and cold in winter

►Over Water Air Masses are:Over Water Air Masses are: MoistMoist Relatively stable temperaturesRelatively stable temperatures

Air Masses MoveAir Masses Move

►Storms are caused when two different Storms are caused when two different air masses make contactair masses make contact

►This causes wind, rapid temperature This causes wind, rapid temperature change and precipitationchange and precipitation

►The line between two air masses is The line between two air masses is called a “front”called a “front”

Warm FrontWarm Front

Warm FrontWarm Front

►Occurs when a warm air mass moves Occurs when a warm air mass moves into a cooler areainto a cooler area

►Warm air rises above the cooler airWarm air rises above the cooler air►This will cause precipitation and fogThis will cause precipitation and fog►Very common in the Spring (April Very common in the Spring (April

showers bring May flowers)showers bring May flowers)

Cold FrontCold Front

Cold FrontCold Front

►Can move twice as fast as warm frontsCan move twice as fast as warm fronts►Cold air masses move to a warmer Cold air masses move to a warmer

areaarea►The cold air forces itself under the The cold air forces itself under the

warmer airwarmer air►As the warm air rises it cools quicklyAs the warm air rises it cools quickly►Can cause severe weather such as Can cause severe weather such as

thunderstormsthunderstorms

CloudsClouds

►Formed when water vapour in the air Formed when water vapour in the air cools and condenses (changes to liquid)cools and condenses (changes to liquid)

►There are three main typesThere are three main types CirrusCirrus CumulusCumulus StratusStratus

►These can combine to form other typesThese can combine to form other types

CirrusCirrus

Cirrus CloudsCirrus Clouds

►Form high in the atmosphere (10-Form high in the atmosphere (10-15kms)15kms)

►Very cold and made up of ice crystalsVery cold and made up of ice crystals►Formed when warm air is pushed very Formed when warm air is pushed very

high upwardshigh upwards►Usually a result of a cold front and Usually a result of a cold front and

means bad weather is comingmeans bad weather is coming

Cumulus CloudsCumulus Clouds

Cumulus CloudsCumulus Clouds

►Most familiar looking clouds Most familiar looking clouds ►Approximately 500 meters above usApproximately 500 meters above us►Made up of water dropletsMade up of water droplets►Usually form when sunshine warms a Usually form when sunshine warms a

pocket of air causing it to rise and pocket of air causing it to rise and condensecondense

►Usually a sign of fair weatherUsually a sign of fair weather

Stratus CloudsStratus Clouds

Stratus CloudsStratus Clouds

►Very low level cloudsVery low level clouds►Sometimes touch the ground (fog)Sometimes touch the ground (fog)►Average 1km thickAverage 1km thick►Build when warm air rises slowly over Build when warm air rises slowly over

cold aircold air►Usually the result of a warm frontUsually the result of a warm front

ForecastingForecasting

►The main goal in studying these The main goal in studying these systems is to accurately predict the systems is to accurately predict the weatherweather

►This is extremely difficult becauseThis is extremely difficult because There are many variables (temp, currents, There are many variables (temp, currents,

etc)etc) These variables can be unpredictableThese variables can be unpredictable Everything is connectedEverything is connected

El NinoEl Nino

►This occurs when the waters of the This occurs when the waters of the South Pacific become warmerSouth Pacific become warmer

►Usually every 3 to 7 yearsUsually every 3 to 7 years►This has drastic global consequencesThis has drastic global consequences

Winds change directionWinds change direction Brings heavy rains to desertsBrings heavy rains to deserts Brings drought to farmlandBrings drought to farmland Very unpredictable patternsVery unpredictable patterns

Jet StreamsJet Streams

►Very high altitude winds (9000-12000 Very high altitude winds (9000-12000 m)m)

►Very fast: more than 300km/hVery fast: more than 300km/h►These dictate the paths storms will These dictate the paths storms will

followfollow►By using weather balloons we can By using weather balloons we can

identify the locations of jet streams and identify the locations of jet streams and therefore predict the directions storms therefore predict the directions storms will gowill go