1. Chapter 25.1= Air Masses Air Mass= a large body of air with a uniform temperature and moisture content. – Forms over a region (large area) – Tropical areas are warm and moist – Polar areas are cold and dry

2. Types of Air Masses Air Masses are classified according to their source region, which also determines temperature and humidity. – Cold label is P (Polar) – Warm label is T (Tropical) – Ocean label is m (maritime) – Land label is c (continental) 4 Main types and combinations of air masses – Maritime Polar (mP) – Maritime Tropical (mT) – Continental Polar (cP) – Continental Tropical (cT)

3. North American Air Masses Maritime Polar Pacific (mP)= formed over North Pacific Ocean. Cool and moist winds. Continental Polar Canadian (cP)= formed over northern Canada. Cool winds during summer, very cold winds in winter. Maritime Polar Atlantic (mP)= formed over North Atlantic Ocean. Cool winds with clouds and fog in summer. Cold winds with clouds and precipitation in winter.

4. North American Air Masses Maritime Tropical Pacific (mT)= form over warm areas of the Pacific Ocean. Summer air usually remains in Pacific, but winter brings heavy rains and thunderstorms to coast. Continental Tropical (cT)= flow over North America only during the summer. Bring clear, dry and very hot weather. Maritime Tropical Gulf, Maritime Tropical Atlantic (mT)= form over the Gulf of Mexico or tropical area of Atlantic Ocean. Mild / cloudy weather in the winter. Summer brings hot, humid, and violent weather.

5. North American Air Masses Image

6. Fronts- a boundary between air masses Cold front- cold air mass arrives and lifts a warm air mass higher in the air. Short, sometimes violent storms are produced. Squall lines, long lines of thunderstorms, occur ahead of fast moving cold fronts. Warm front- a warm air mass gradually overtakes a cold air mass. The warm air rises over the cold air while a lengthy and warm storm occurs. Occluded front- cold air front arrives and quickly overtakes a warm air front, pushing the warm air higher. Stationary front- A warm and cold air mass meet but neither is able to overtake the other. Weather is similar to warm front conditions.

7. Front Symbols

8. Cold Front – wedge shape forcing warm air upward

9. Warm Front – warm air travels up cold air like a ramp

11. Stationary Front= it’s a draw!

12. Thunderstorms Thunderstorm formation requires three things: Moisture - to form clouds and rain. Unstable Air - relatively warm air that can rise rapidly. Lift - things like fronts, sea breezes and mountains can lift air to help form thunderstorms.

13. Thunderstorm Hazards – Hail – Damaging Winds – Tornados – Flash Floods http://www.youtube.com/watch?feature=player_detailpage&v=DNgpI03nWFM http://www.youtube.com/watch?feature=player_detailpage&v=5pyvf4Nr9CE http://www.youtube.com/watch?feature=player_detailpage&v=I5VRPgybP2M

14. Formation of a Tornado The strongest tornadoes are often produced from large, single celled, and rotating thunderstorms termed Super cell Thunderstorms.

15. Tornadoes Tornadoes are the most violent type of storm, with wind speeds reaching up to 300 miles per hour. Tornadoes develop from powerful thunderstorms and appear as rotating, funnel- shaped clouds. Tornadoes cause damage when they touch down on the ground. The path of a tornado can range from one mile wide to 50 miles long.

17. Minimal Tornado F0, F1 F0, F1 - 67% of S.C. TX Tornadoes - 67% of S.C. TX Tornadoes - Causes 5% of all deaths - Causes 5% of all deaths - Life span 1 to 2 minutes - Life span 1 to 2 minutes - Path length less than 1 mile - Path length less than 1 mile - Path width less than 100 yards - Path width less than 100 yards - Wind speeds up to 110 mph - Wind speeds up to 110 mph

18. Strong Tornado F2, F3 F2, F3 - 30% of S.C. TX Tornadoes - 30% of S.C. TX Tornadoes - Causes 30% of all deaths - Causes 30% of all deaths - Life span 15 to 20 minutes - Path up to 15 miles - Path width up to 500 yards - Path width up to 500 yards - Wind speeds up to 200 mph - Wind speeds up to 200 mph

19. Violent Tornado F4, F5 F4, F5 - 3% of S.C. TX Tornadoes - 3% of S.C. TX Tornadoes - Causes 65% of all deaths - Causes 65% of all deaths - Life span to several hours - Life span to several hours - Path length dozens of miles - Path length dozens of miles - Path width to 1 1/ 2 miles - Path width to 1 1/ 2 miles - Wind speeds over 300 mph - Wind speeds over 300 mph

20. Tornado Safety Tips Prepare for tornadoes by gathering emergency supplies including food, water, medications, batteries, flashlights, important documents, road maps, and a full tank of gasoline. When a tornado approaches, anyone in its path should take shelter indoors—preferably in a basement or an interior first-floor room or hallway. Avoid windows and seek additional protection by getting underneath large, solid pieces of furniture. Avoid automobiles and mobile homes, which provide almost no protection from tornadoes. Those caught outside should lie flat in a depression or on other low ground and wait for the storm to pass.

21. Hurricanes The United States Weather Bureau calls a wind a hurricane when it blows as fast as 74 miles an hour. Severe tropical storms developing over warm water. Hurricanes may have a diameter of 400 to 500 miles (640-800 kilometers). The “eye” of a hurricane can be up to 20 miles across. The weather in the “eye” is calm with low winds and clear skies. Many hurricanes cause severe flooding.

23. Hurricane Hotspots

24. Hurricane Safety Tips Before a Hurricane To prepare for a hurricane, you should take the following measures: Build an emergency kit and make a family communications plan Know your surroundings. Learn the elevation level of your property. Identify levees and dams in your area. Learn community hurricane evacuation routes. Cover all of your home’s windows. Be sure trees and shrubs around your home are well trimmed. Clear loose and clogged rain gutters and downspouts. Reinforce your garage doors Plan to bring in all outdoor furniture, decorations, garbage cans, etc. Determine how and where to secure your boat. Install a generator for emergencies. If in a high-rise building, be prepared to take shelter below the 10th floor. Consider building a safe room.

25. Weather Forecasting Instruments Anemometers are used to measure wind speed and the direction that it is blowing. A wireless weather station is capable of measuring wind speed, wind direction, temperature, humidity, rainfall and barometric pressure.

26. Weather Symbols

28. Weather Station

29. Practice Quiz 1)What is an air mass? 2)What are the 4 main types and combinations of air masses? 3)What are squall lines? 4)List the 4 types of fronts with their characteristics. 5)What is the major cause of death associated with tornadoes and hurricanes? 6)List two tornado safety tips people should follow. 7)What instruments are used to measure weather? 8)How is wind direction represented on a weather station? 9)What scales are used to measure the power of tornadoes and hurricanes? 10)What are three ways to prepare for a hurricane?