What are fronts ?

Air Masses• a body of air extending hundreds or thousands of miles sideways and

sometimes as high as the stratosphere and having nearly the same conditions of temperature and humidity.

Types of air masses

Humid Air masses

Dry Air masses

Air Fronts• When air masses move across the surface of the

earth they may collide.

• These collisions happen halfway between one of the poles and the equator.

• The 2 air masses don’t mix much when they collide.

• Each keeps its own temperature ,humidity and pressure.

• As a result ,a boundary forms, this boundary is called “Front”.

Types of Air FrontsScientists classify fronts by the characteristics and movements

of the two air masses.

1-Warm FrontWhen a warm air mass moves into an area of

cooler air ,the boundary between the air is called

“Warm front”

The warmer ,less dense air slides up over the cooler denser air in a wide ,gentle slope

• As the warmer air cools ,its relative humidity increases, and the water vapor condenses into clouds.

• A warm front usually results in steady rain .

2)Cold Front• When a cold air mass moves into an area of

warmer air , the boundary between air masses is called “Cold front”

• The colder ,denser air slides under the warmer air is pushed up .

• As the warmer air cools ,the water vapor condenses and form clouds that brings precipitation

3)Occluded front

This produces a wedge of warm air between 2 masses of cold air .The formation of an occluded front often indicates that a storm will happen but will not last for long.