• 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
• 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
• Each keeps its own temperature ,humidity and
• As a result ,a boundary forms, this boundary is
Types of Air Fronts
Scientists classify fronts by the characteristics and movements
of the two air masses.
When a warm air mass moves into an area of
cooler air ,the boundary between the air is
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
• A warm front usually results in steady rain .
2)Colda 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
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.