Fronts and Air Masses

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  • 1. FrontsFronts
  • 2. Fronts and Air MassesFronts and Air Masses  Air massesAir masses: a huge: a huge body of air withbody of air with similarsimilar temperature,temperature, humidityhumidity, and, and pressurepressure..  In America, we haveIn America, we have four air masses thatfour air masses that affect us. They areaffect us. They are based onbased on temperaturetemperature andand humidity.humidity.
  • 3. Air Masses and Global WindsAir Masses and Global Winds  In America air masses are pushed by theIn America air masses are pushed by the prevailing westerlies.prevailing westerlies.  So they tend to moveSo they tend to move westwest toto easteast..
  • 4. Types of Air MassesTypes of Air Masses  TropicalTropical: form over the: form over the tropics, so they aretropics, so they are warmwarm and will haveand will have lowlow air pressure.air pressure.  PolarPolar: form north/south: form north/south of 50º latitude. So theyof 50º latitude. So they areare coldcold and will haveand will have highhigh pressurepressure..  MaritimeMaritime: form over the: form over the oceans so they areoceans so they are humidhumid..  ContinentalContinental: form over: form over the middle ofthe middle of continentscontinents (land) so they are dry.(land) so they are dry.
  • 5. Air Masses ComparedAir Masses Compared TypeType TempTemp HumidityHumidity PressurePressure MaritimeMaritime tropicaltropical (mT)(mT) WarmWarm HumidHumid LowLow MaritimeMaritime polar (mP)polar (mP) ColdCold HumidHumid HighHigh ContinentalContinental tropical (cT)tropical (cT) WarmWarm DryDry LowLow ContinentalContinental polar (cP)polar (cP) ColdCold DryDry highhigh
  • 6. Weather FrontsWeather Fronts  FrontsFronts: where two: where two air masses meet andair masses meet and don’t mix.don’t mix.  Front is a militaryFront is a military term where twoterm where two armies meet toarmies meet to fight.fight.  The collision ofThe collision of fronts often causesfronts often causes storms andstorms and changeable weather.changeable weather.  There areThere are fourfour kinds of fronts.kinds of fronts.
  • 7. Cold FrontsCold Fronts  ColdCold fronts have cold,fronts have cold, dense air.dense air.  They will slide underThey will slide under warm, less dense air.warm, less dense air.  So theSo the warmwarm air isair is pushed up, whichpushed up, which causes it tocauses it to coolcool..  This means it can holdThis means it can hold lessless waterwater vapor, sovapor, so cloudsclouds form as itform as it reaches itsreaches its dew pointdew point..  This can causeThis can cause rainrain andand storms behindstorms behind thethe front.front.  They move quickly, andThey move quickly, and bring cool, dry airbring cool, dry air after the front passes.after the front passes.
  • 8. Warm FrontsWarm Fronts  MovingMoving warmwarm air collides withair collides with coldcold air.air.  Tend to move moreTend to move more slowlyslowly than cold fronts.than cold fronts.  Can bring cloudy skies, showers, and light rainCan bring cloudy skies, showers, and light rain preceding the frontpreceding the front..  Weather will beWeather will be warmwarm andand humidhumid after itafter it passes.passes.
  • 9. StationaryStationary FrontsFronts  Occur when cold andOccur when cold and warm fronts meetwarm fronts meet and neither is strongand neither is strong enough to force theenough to force the other to move.other to move.  It is aIt is a “standoff.”“standoff.”  The warm air willThe warm air will condensecondense and formand form rain, fog, snow, orrain, fog, snow, or clouds.clouds.  Can causeCan cause manymany daysdays ofof wetwet weather.weather.
  • 10. OccludedOccluded FrontsFronts  Occur when aOccur when a warmwarm airair mass ismass is trappedtrapped between two cold airbetween two cold air masses.masses.  TheThe warmwarm air is pushedair is pushed up when the two coldup when the two cold air masses meet.air masses meet.  It is cut off from theIt is cut off from the ground, orground, or occludedoccluded..  Tend to produce strongTend to produce strong thunderstormsthunderstorms..
  • 11. Weather Map SymbolsWeather Map Symbols  These are theThese are the symbols yousymbols you would see on awould see on a weather map.weather map.  The arrows orThe arrows or bumps point inbumps point in the directionthe direction the front isthe front is moving.moving.
  • 12. Low Pressure AreasLow Pressure Areas  Low pressure areas willLow pressure areas will have warm, rising air.have warm, rising air.  Cool air around it willCool air around it will spiral in counterspiral in counter clockwise (Coriolisclockwise (Coriolis effect).effect).  As the air rises, it coolsAs the air rises, it cools and reaches its dewand reaches its dew point.point.  So clouds and rain willSo clouds and rain will form.form.  Called cyclones from aCalled cyclones from a Greek word meaningGreek word meaning wheel.wheel.
  • 13. High Pressure AreasHigh Pressure Areas  High pressure centers ofHigh pressure centers of dry air.dry air.  Spiral outward towardsSpiral outward towards areas of lower pressure.areas of lower pressure.  Coriolis effect causesCoriolis effect causes them to spiral clockwisethem to spiral clockwise in the Northernin the Northern Hemisphere.Hemisphere.  Made of cool, falling air,Made of cool, falling air, so its relative humidityso its relative humidity drops.drops.  Produces clear, dryProduces clear, dry weather.weather.  Called anticyclones.Called anticyclones.