2.  Bodies of air that bring distinctive weather features to the country.  A mass of air in air that is very uniform in temperature, pressure, and humidity. Polar = cold Tropical = warm Maritime = moist Continental = dry Air Masses

3.  May cover several millions of square kilometers and extend vertically throughout the troposphere

4. Pressure of Air Masses Air Pressure = weight of air acting on an area Warm Air has more KE and spreads out more. Therefore, it’s less dense and has less weight. This means less pressure. Warm Air Masses are less dense and have Lower Pressure

5. Pressure Systems  Uneven heating of the Earth’s surface causes differences in air pressure Warm Air  Low Pressure System Cold Air  High Pressure System

6. Weather Map: Fronts, Systems, Jet stream

7. Weather Fronts A front is the transition zone between two air masses of different density. Fronts extend not only in the horizontal direction, but in the vertical as well.

8. Cold Front & Air Masses

9. Global Wind Patterns

10. Cold Front on a Weather Map

11. Warm Front on a Weather Map

12. Occluded (Stationary) Fronts

13. Wind Patterns  Air flows from areas of high pressure into those of low pressure  Northern Hemisphere: air flow from areas of high to low pressure is deflected to the right; producing a clockwise circulation around an area of High pressure.  Counter-clockwise circulation around an area of Low pressure.

14. Wind Circulation Patterns

15. Weather Forecasting  Tools Used: Thermometer (temperature) Barometer (pressure) Hygrometer (humidity) Radar (storm & cloud movement) Satellite imagery (storm & cloud movement)  National Weather Service Boise Site:  http://www.wrh.noaa.gov/boi/ http://www.wrh.noaa.gov/boi/  Weather Channel Site:  http://www.weather.com/ http://www.weather.com/

16. Weather Maps

17. Climate  Average of all weather conditions in area over a long time Ex: temperature, precipitation  Climate is cyclically influenced by ocean currents & temperatures El Niño & La Niña  These variations alter: surface wind surface ocean temperatures deep ocean temperatures

18. Climate Cycles Caused by variations in ocean currents & temperatures ○ Cycles occur every 3-7 years ○ El Niño: characterized by unusually warm ocean temperatures in the Equatorial Pacific ○ La Niña: characterized by unusually coldocean temperatures in the Equatorial Pacific

19. Normal vs. El Niño Ocean Temperatures Unusually warm ocean temperatures in the Equatorial Pacific Winters are warmer than normal in the Northern States & cooler than normal in the Southern States

20. Normal vs. La Niña Ocean Temperatures Unusually cold ocean temperatures in the Equatorial Pacific Winters are cooler than normal in the Northwest & warmer than normal in the Southeast

21. Cloud Characterization  Clouds are characterized by: 1. Height above the ground a) Cirro b) Alto c) Nimbo 2. Type of cloud a) Cirrus b) Cumulus c) Stratus – any cloud type can form layers

22. Cloud Levels & Types

25. Layers of the Atmosphere