What is weather

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

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

15. 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 .

16. How fronts are represented on the weather map?

17. 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.)

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

19. 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.

20. They curve clockwise in the Northern Hemisphere and counter clockwise in Southern Hemisphere .

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

22. 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.

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