AIR MASSES & FRONTS

Air masses can travel away from the regions where they form. They move with the global pattern of winds. In most of the

United States, air masses generally move from west to east. They may move along

with the jet stream in more complex and changing patterns.

Air Masses

• A large body of air with similar temperature and moisture.

• Air masses form over large bodies of water or land masses and are named by where they form…over land-continental or over water-maritime and also named for where they originate from-near the tropic-tropical and from near the poles-polar

Description of air masses:

–Continental polar (cP)- cool (cold) and dry• Continental arctic-(cA) type of continental polar mass that is very

cold & dry-forms over the arctic circle

–Continental tropical (cT)- warm (hot) and dry–Maritime polar (mP)- humid (wet) and cold;

unstable-low pressure–Maritime tropical (mT)- humid (wet) and

warm; unstable-low pressure

Interactive Air Mass Link

• http://www.usatoday.com/weather/tg/wamsorce/wamsorce.htm

FRONTS

• The boundaries between two air masses; the leading edge of an air mass

• Different types of weather are brought about or left behind after the different fronts-warm, cold, stationary, or occluded

Cold Fronts• A cold air mass is replacing a warm air mass.• Shown on a weather map by a blue line with

triangles pointing the direction in which the cool air (front) is moving.

• Low air pressure is found along the leading edge of a cold front which is why there is a chance of thunderstorms or severe weather when they pass through.

• High air pressure is associated with cold fronts which means sunny and fair weather.

Weather Map

Warm Fronts

• A warm air mass replacing a cold (cooler) air mass.

• Shown on a weather map by a red line with half circles pointing the direction in which the warm air (front) is moving.

• Low pressure is associated with warm fronts which means cloudy, overcast, drizzly, and possibly rainy weather.

Weather Map

Comparing Warm and Cold Fronts• Cold fronts move faster than warm fronts. • The weather activity in a cold front is often violent and

happens directly at the front.• Cold fronts have sudden gusty winds high in the air

creating turbulence .• Cold fronts bring beautiful weather while warm

fronts can bring dreary weather. • The weather activity in a warm front generally

happens before the front passes through an area. Steady rain or drizzle may fall for a long period of time.

• In a warm front the cloud formation is very low often creating situations of poor visibility.

Occluded Front

•When a warm front is trapped by (between) two cold fronts.

•Shown on a weather map by a purple line with alternating triangles and half circles pointing the direction the front is moving.

Stationary Front

• A front that is not moving or is moving very slowly.

• Shown on a weather map with alternating red semicircles pointing away from the warm air and blue triangles pointing away from the cold air.

• Stationary fronts can cause many days of unchanged weather conditions-usually cloudy, rainy, dreary weather.

Weather Map

For current weather map….

• http://www.weather.com/maps/maptype/currentweatherusnational/uscurrentweather_large.html

Practice & Assess

• Practice: Air Masses Over North America Worksheet

• Assessment: Air Masses Practice Quiz• http://www.quia.com/quiz/278988.html?

AP_rand=2099466504