Air Masses and Fronts

Definition Air mass- huge section of the lower troposphere that have the same kind of weather (temperature and humidity) throughout.

Properties of Air Masses cause changes in the weather are classified by where they form form over oceans and land amount of moisture (humidity) depends on where the mass develops. named for source region or places of origin

Source Regions Source regions for cold air masses are polar areas and are labeled P Source regions for very cold air are arctic areas and are labeled A Source regions for warm air are masses are tropical areas and are labeled T Source regions over oceans are called maritime and are labeled m , they are moist Source regions over land are called continental and are labeled c , they are dry

Types of air masses 5 major types of air masses mP- maritime polar is cold and humid brings cooler temperatures to Eastern US Brings fog to California and western states

Maritime tropical mT maritime tropical holds warm moist air in summer- brings very hot, humid weather in winter- if this air meets with cold air mass, rain or snow will fall

Continental tropical cT continental tropical originates in tropical land areas and desert areas of SW US are hot and dry *Least effects the US

Continental polar cP continental polar originates over land in Canada are cold and dry causes very cold temp in the US in the winter

Continental arctic cA continental arctic very cold and dry come from ice covered Arctic regions

Air masses change as they move from their source region. they diverge from areas of high pressure and converge in areas of low pressure are very large and take several days to pass through a region. Fast moving air masses spend less time over any one area and bring more extreme weather

Fronts boundary between air masses that have different temp. and humidity. when two air masses meet, a front forms an approaching front means a change in weather, almost always brings ppt. four types of fronts forceful lifting- when two contrasting air masses meet, the lighter warmer of the two is lifted or rises above the cooler, denser air mass. MAJOR CAUSE OF PPT in the US. (large pressure gradient)

Cold Front forms when a mass of cold air meets and replaces a mass of warm air *Moves more quickly than a warm front cold air forces the warm air mass upward violent storms are associated with cold front has a steep slope often forms a line of thunderstorms called a squall line (*lightening , hail, cumulonimbus clouds, strong wind, large pressure gradient)

Warm Front forms when a mass of warm air advances into an area occupied by a cold air mass Drizzle may accompany a warm front hot humid, weather follows gentle slope, *small pressure gradient, weak winds, nimbostratus clouds.

Occluded Front forms when cold front overtakes a warm front (cold front travels faster then a warm front) warm air is *pushed upward and the warm air meets cool air weather is complex and extreme (*flash floods)

Stationary Front warm air mass meets a cold air mass no movement occurs rain may fall for days (*major flood events)

Cyclone An area of low pressure containing rising warm air Convergence and forceful lifting create clouds. cool air moves in to take the place of rising warm air move in counterclockwise direction rainy, stormy weather *Closely spaced isobars *

Cyclone Development A wavelike kink develops- warm air is pushing N, (warm front) cool air is pushing S (cold front) Cold front moves more rapidly and overtakes warm front producing unstable air and cloud development Occluded front is produced, moves *CCW, stormy, close isobars)

Cyclone

Anticyclone high pressure area containing cold dry air clockwise direction clear dry weather isobars usually *farther apart , winds are weaker

Ways that air can be lifted: Convective-occurs in areas where there is a large difference in heating. Orographic- air forced to rise over mountains Frontal- occurs along boundary between air masses.