1. Billion Dollar US Weather disasters Chapter 25 Weather 2013: Category 4 Tornado, Oklahoma City, Moore & Newcastle. >90 killed, including 20 children. 2012: National drought. 123 deaths, $40 billion in damages SE & Ohio valley. 75 tornadoes, $4 billion in damages, 42 deaths Texas. 22 tornadoes, $1.3 billion in damages Midwest. 98 tornadoes hit OK, KS, NE, IA, $2 billion, 6 deaths Midwest. 38 tornadoes, large hail, Hit StL hard, $4 billion, 1 death 27 tornadoes over several states, $2.5 billion, 1 death SW. 25 tornadoes, hail damage over $1 billion in CO alone Midwest. $4 billion, 28 deaths Hurricane Isaac. $2.3 billion damages, 42 deaths Western wildfires. $9.1 million acres, est. between $1-2 billion Hurricane Sandy. Est. $82 billion, 132 deaths 2011: Over 55 billion in damages, 646 deaths (Most deadly year in a decade)

2. 25.1 – Air Masses Air Mass – large body of air with uniform temperature and moisture content. May be thousands of km in diameter.

3. Polar Air Masses Continental Polar Canadian (cP) – form over land covered in ice and snow Maritime Polar Pacific (mP) – form over north Pacific; Aleutian Islands Maritime Polar Atlantic (mA) – form over north Atlantic; between Greenland and Iceland

4. Tropical Air Masses Continental Tropical (cT) – flow over N.A. only in summer; hot dry air to the SW Maritime Tropical Gulf & Atlantic (mT) – form over the Gulf of Mexico & tropical N. Atlantic; move northward over eastern US; bring mild winters, and hot, humid summers with thunderstorms and hurricanes Maritime Tropical Pacific (mT) - form over the warm areas of the N. Pacific; rarely reach the coast

5. 25.2 Fronts Front – occur where there are two unlike air masses Density keeps the air separate. (cold vs. warm) May be several hundred km to several thousand km long. Fronts do not exist in the tropics because there is not temperature differences.

6. Cold front Warm front http://www.youtube.com/watch?v=bN7E6FCuMbY Squall line – long line of heavy thunder storms; may occur just ahead of fast moving cold front (write down for homework!)

7. Stationary Front Two masses meet, and neither one is displaced Winds blowing parallel to the front (not perpendicular) help it stay in place Symbols point toward air type.

8. Occluded front Sometimes a cold front follows right behind a warm front. Because cold fronts move faster, the cold overtakes the warm. At an occluded front, the cold air mass from the cold front meets the cool air that was ahead of the warm front. The warm air rises as these air masses come together. Usually forms around areas of low pressure.

9. Polar Front Boundary where cold polar air meets the warmer air of middle latitudes. Circles the earth between 40° – 60° latitude in each hemisphere. p. 503-4 Moves toward equator in winter. Recedes in the summer.

10. Wave Cyclone - forms at the boundary of a polar front. Warm and Cold winds blow in opposite directions. An intensified low-pressure region forms in the center. Page 503-504

11. Hurricanes – most severe tropical storm, with wind speeds starting at 120 km/hr. Develop over warm, tropical oceans Most common in the western Pacific (20/yr) where they are called typhoons

12. Hurricanes & Typhoons Very warm, moist air rises off the water. As the air rises, it cools and condenses, releasing energy, increasing the force of rising air. The eye itself is a region of calm, clear, sinking air. An average hurricane has the KE (wind energy) of about half the world-wide electrical generating capacity.

13. Thunderstorms Storm accompanied by thunder, lightning, and strong winds. Occur when warm, moist air (mT) is heated and rises. Occur most often in late afternoon or early evening.

14. Tornadoes The smallest, most violent and shortest-lived storm. Dallas, TX April 2012 https://www.youtube.com/watch?v=uSs45dJGOlE https://www.youtube.com/watch?v=0L-XExpb3pY Moore, OK 2013 EF5 p. 507-8 A tornado over the ocean is called a “Water Spout” http://www.telegraph.co.uk/news/worldnews/australiaandthepacific/australia/9686072/Rare-waterspout-forms-off-Australia.html