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Air Masses &Fronts
Air Masses
• When a large bubble of air remains over a specific area long enough to take on temperature and humidity characteristics of the region, it is an air mass
• So, air masses are identified by their temperature and moisture content.
• For temperature air masses are either
• Tropical ( T) relatively warm
• Polar (P) relatively cool
• For moisture content, air masses are
• Marine/Maritime (m) relatively moist
• Formed over ocean
• Continental (c) relatively dry
• Formed over dry land
• Air masses are then identified by these symbols
• an air mass identified as cP is relatively cool and dry
• an air mass identified as mT is relatively warm and moist
Identifying air masses
4 basic air masses
• cP- continental polar = cool dry
• mP - maritime polar = cool moist
• cT - continental tropical = warm dry
• mT - maritime tropical = warm moist
• During winter, an even colder air mass occasionally enters the northern US.
• This bitterly cold air mass is called continental arctic (cA)
• It sets record cold temperatures when it enters area
Air Mass Source Regions
• Air masses float across the Earth’s surface
• The type of air mass sitting over you determines the weather condition
• By knowing what air mass is moving into your location you can predict general weather conditions.
• When 2 air masses interact with each other a front is produced
• A front is simply the boundary between two air masses
Weather Fronts
• occurs when cold air intrudes on warm air
• warm air is lifted relatively rapidly
• forms cumulonimbus clouds and thunderstorm activity
• typically heavy rain over a relatively small area
• cold fronts are identified on a map as a line with triangles on it
Cold Front
• Warm air intrudes on cold air
• warm air rises as shallow gradient above cold air
• lead to distinct formation of clouds. Early stages form cirrus clouds
• As front continues to approach clouds get heavier and lower
• Usually bring moderate precipitation over wide area
• On weather map as line with red semicircles
Warm front
Video on Discovery
StreamingWatch segments 9-14
• A stationary front is formed when 2 air masses come together, but neither displaces the other
• Represented by alternation blue triangles and red semicircles on a line.
• The blue triangles point toward warm front
• Red semicircle point toward cold front
Stationary
Front
• When cold air mass rapidly overtakes warm air mass and traps warm air between 2 cold air masses
• This event usually identified with a mid-latitude cyclone
• See heavy cloud cover and precipitation of wide area
• Provides much weather for central US
Occluded
Front
• H – High Pressure system – clear skies and calm
winds
• L- Low Pressure System – storms, rain, clouds…
Lousy weather
• Line is drawn to show position of air mass and
then symbols positioned to show directional
movement of air mass.
• Isobars: lines that connect air pressures that are
the same.
Weather Maps
Warm Front
Cold Front
Stationary Front
Occluded Front