When a large body of air movesit causes weather changes.Air massLarge body of air.
Air massescan be:Hot air mass Cold air massAll of an air mass has the sametemperature and same amount ofmoisture level (amount of water inthe air).
Blue arrows are cold air massesRed arrows are hot air masses
Temperature and moisture level depend onwhere the air masses where formed.Dry airmassFormedover landWet air massFormed overoceans orseasHot airmassCome fromthe southCold airmassCome fromthe north
Type of weather caused by different airmasses:Cold, dryair massesCoolweather, withlittle or noprecipitationWarm, moistair massesLot ofprecipitationWarm, dryair massesWarmweather +little or noprecipitationCold, Wetair massesSnow
Air massesStay separateWhy?Because warm air is lighter than coldair.So, warm air masses are pushedupward and cold air masses sink.
Air massesmoveThe border between one air mass andthe other is called a front.
Air frontscan be:HotfrontColdFrontStationaryfront
1) Cold FrontCold air moves under warm air.Warm air mass moves up and cools down.Water vapor condenses and moves up.It might rain or thunderstorms develop alongthe frontAs the cold air mass moves forward theweather becomes cooler.
2) Warm FrontWarm air moves slides over cold air.Warm fronts moves slowly.Steady rain instead of thunderstorms.Warm fronts are followed by clear, warmweather.
3) Stationary frontA front that stays in one place for many daysHappens when two air masses do not haveenough energy to move.Steady rain instead of thunderstorms.Weather along the stationary front is oftencloudy and wetThis kind of front can leave inches of snow orcause flooding.