1. Weather Patterns Air Masses and Fronts

2. Types of Fronts Cold front – a cold air mass overtakes a warm air mass ▫Type of Weather: clouds, possibly storms with heavy precipitation (rain or snow) Warm front – warm air mass overtakes a cold air mass ▫Type of Weather: clouds, light precipitation (rain or snow)

3. Types of Fronts Occluded front – a warm air mass is caught between 2 cold air masses ▫Type of Weather: weather turn cloudy and rain or snow my fall; precipitation Stationary front – cold & warm air masses meet, but neither can move the other ▫Type of Weather: clouds, precipitation (snow/rain)

4. Types of Air Masses Four major types of air masses influence the weather in NA: maritime tropical, continental tropical, maritime polar, and continental polar Tropical, or warm, air masses form in the tropics and have low pressure Polar, or cold, air masses form north of 50 degree N latitude and south of 50 degree S latitude

5. Types of Air Masses Maritime air masses form over oceans Continental air masses for over land

6. How Air Masses Move In the continental US, air masses are commonly moved by the prevailing westerlies and jet streams. Prevailing Westerlies Jet Streams Fronts

7. Cyclones & Anticyclones Cyclones have a center of low air pressure Cyclones and decreasing air pressure are associated with clouds, wind, and precipitation Anticyclones are high pressure centers of dry air The descending air in an anticyclone generally cause dry, clear weather.

8. News Report Suppose you are a TV weather reporter covering a severe thunderstorm. Write a brief report to explain to viewers the conditions that caused the thunderstorm.