What Causes Wind?Air is a fluid – it moves easilyMovement of air caused by changing air pressureair pressure

Wind is movement of air from high pressure to low pressureigh pressure to low pressure

Air Movement

Types of Air MassesAn air mass forms when a large

amount of air stays in the same place over an area

Continental air masses form over land and are dry

Maritime air masses form over water and are moist

Polar air masses are coldTropical air masses are warm

Types of Air MassesThere 4 air masses affecting North

AmericacT- continental tropicalcP – continental polarmT – maritime tropicalmP – maritime polar

FrontsAir masses move and bump into

each otherFronts appear at the edges of two

air masses where they are colliding with each other

FrontsThere are 4 types of fronts:

Cold fronts Stationary frontsWarm fronts Occluded fronts

Cold frontOccurs when a cold air mass

overtakes a warm air massCold air forces warm air to rise

quicklyResulting in strong winds,

thunderstorms, and large amounts of precipitation

Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction.

http://www.suu.edu/faculty/colberg/hazards/weather/05_cnWfronts.html

Cold Front Diagrams

Warm FrontsOccurs when a warm air mass overtakes a cold air mass

Warm air slowly rises over the cold air

Starts with steady rain (8-12 hours) but eventually clears when temperatures rise

Warm fronts tend to move slowly are far less violent then cold fronts

After warm front passes, weather becomes warm and humid, but generally clear

Warm Front

Warm Front Diagrams

Stationary FrontWhen neither air mass can move the other

Similar to warm fronts and can remain in same place days

Light wind and precipitation occur across entire region affected

Occluded frontWhen a warm air mass gets trapped between

two cold air massesStrong winds and heavy precipitation occur