1. What is
weather?

2. Weather
• Weather it is the condition of the atmosphere
at a particular time and place .

3. 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.

4. Types of air masses
Humid Air masses
Dry Air masses

5. Humidity
It is the amount of water vapor in the air .

6. Pressure
• It is the weight of air pressing on a unit area.

7. • The difference of air pressure is due to
unequal heating of the Earth.
• Warm air masses have fewer air molecules
than cold air masses.
Therefore , they are less dense having lower air
pressure.

8. 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”.

9. Types of Air Fronts
Scientists classify fronts by the
characteristics and movements of the two
air masses.

10. 1-Warm Front
When 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

11. • As the warmer air cools ,its relative humidity
increases, and the water vapor condenses
into clouds.
• A warm front usually results in steady rain .

12. 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 .

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

15. Stationary front
• The boundary between 2 air masses that are not
moving against each other is called
“Stationary front”.

16. Some of the warmer air mixes with cooler air
,causing clouds to form .
As the clouds are pushed up ,they cool and
produce light rain or snow .
Because the front is not moving ,the
precipitation can last for a long time .

17. How fronts are represented
on the weather map?

18. Global wind pattern
• Wind is the movement of air from an area of
higher pressure to an area of lower pressure.
(Remember: Differences in air pressure is due to
uneven heating of the earth.)

19. Global Winds
• They are winds that blow across long
distances in a predictable patterns.

20. • Each of these winds carry air masses from one
region to another .
• Each of these winds always blows in the same
direction
• Global winds don’t follow a straight path as
they blow from poles toward the equator or
from the equator towards the poles.

21. • They curve clockwise in the Northern
Hemisphere and counter clockwise in
Southern Hemisphere .

22. This curving of the winds is called
“Coriolis effect”

23. Jet Stream
• Is a band of very strong wind that blows from
east to west high in the atmosphere ,usually
above 6000m .
• Jet streams from along boundaries of large air
masses when warm air from the tropics meets
air from the poles.

24. • The sudden temperature change causes a huge
difference in air pressure .
• This results in wind speeds of up to 498km/hr