1. The Causes of Weather Meteorology is the study of atmospheric phenomena. The Causes of Weather

3. Weather and Climate Weather is the current state of the atmosphere, including short-term variations that affect our lives. The Causes of Weather Climate describes the average weather over a long period of time and is usually averaged over the course of 30 years or more. Meteorology, weather, and climate are related.

4. A Question of Balance The Causes of Weather

5. Air Masses An air mass is a large body of air that takes on the characteristics of the area over which it forms. The Causes of Weather

6. Air Masses Classifying Air Masses The Causes of Weather – Air masses are classified according to their source regions. warm and dry continental tropical (cT) warm and humid maritime tropical (mT) cold and dry continental polar (cP) cold and humid maritime polar (mP) arctic (A)

7. Air Masses Classifying Air Masses The Causes of Weather – Each of the major air masses that affects weather in the United States has a similar temperature and moisture content as the area over which it formed.

8. Air Masses Air Mass Modification The Causes of Weather

9. Weather Systems Coriolis Effect- Deflects moving particles such as air to the right above the equator; caused by Earth’s rotation and combines with the heat imbalance founded on Earth to create the trade winds, polar easterlies, and prevailing westerlies. Colder air to warmer areas and warmer air to colder areas.

10. Wind Systems Trade Winds (Hadley Cell)-30 degrees North and South latitude, air sinks, warms, and moves to equator in a westerly direction. Prevailing Westerlies- flows between 30 and 60 degrees North and South latitude, in a circulation pattern opposite that of the Trade Winds. Surface winds move towards the poles in an easterly direction. Wind blows from the West. Responsible for the movement of our weather in the U.S. Polar Easterlies-lies between 60 degrees latitude and the poles. Flows from the northeast to the southwest in the Northern Hemisphere. Opposite in Southern Hemisphere. Bring COLD air.

11. WIND SYSTEMS

12. High Pressure System Generally associated with fair, sunny weather As high pressure is an area of sinking air, and air tends to dry out as it sinks, leaving sunny skies

13. High Pressure Animation http://www.juicygeography.co.uk/downloads/flash/highpressu re.swf http://www.juicygeography.co.uk/downloads/flash/highpressu re.swf

14. Low Pressure System Generally cloudy/rainy areas -- where strong areas of low pressure bring our stormiest weather This is because it's an area of rising air, and as air rises, it condenses into clouds and rain Air moves from higher pressure to lower pressure, so if you have a high and a low nearby, it can be windy as air rushes between the two

15. Low Pressure Animation http://www.juicygeography.co.uk/downloads/flash/lowpressur e.swf http://www.juicygeography.co.uk/downloads/flash/lowpressur e.swf

16. Fronts When two air masses that have different properties meet, they do not mix easily. A boundary forms between the two air masses. This boundary is called a front. There are four types of fronts: cold fronts, warm fronts, occluded fronts and stationary fronts. The weather at a front is usually unsettled and stormy.

17. Cold Front A cold front forms when a mass of cold air meets and pushes under a mass of warm air. The cold air mass forces its way underneath the warm air mass and pushes it upward. Violent storms are associated with a cold front. Fair, cool weather usually follows.

18. Warm Front A warm front forms when a mass of warm air overtakes a cold air mass and moves over it. Rain and showers usually accompany a warm front. Hot, humid weather usually follows.

19. Occluded Front A cold front travels faster than a warm front. When a cold front overtakes a warm front, an occluded front forms. As the warm air is pushed upward, the cold air meets cool air. An occluded front may also occur when cool air overtakes a cold front and warm air is pushed upward. An occluded front produces less extreme weather than a cold or warm front.

20. Stationary Front When a warm air mass meets a cold air mass and no movement occurs, a stationary front forms. Rain may fall in an area for many days when a stationary front is in place.