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