1. Severe Storms

2. Thunderstorms Occur in warm, moist air masses and along fronts. Sinking rain, cooled air, and strong updrafts of warm air cause strong winds. If winds reach 89 km/h or faster, it is a severe thunderstorm. Flash floods, strong winds, hail.

3. Thunderstorms

4. Lightning In a storm cloud, warm air is lifted rapidly as cooler air sinks. This movement causes different parts of the cloud to become oppositely charged. When the current flows between opposite charges, lightning flashes. Occurs in 3 places: within a cloud, between clouds, cloud and the ground.

5. Lightning

6. Thunder Results from rapid heating of air around lightning. (Lightning is 30,000 degrees celsius.. 5x the surface of the sun!!) The extreme heat causes air around the lightning to expand rapidly. Then it cools and contracts. The rapid movement of molecules forms sound waves heard as thunder.

7. Thunder

8. Tornadoes A violently rotating column of air in contact with the ground. In severe thunderstorms, wind at different levels blow at different direction and speed. This is called wind shear. Rips apart building, uproot trees, blow through glass. Can lift animals, cars and houses in the air.

9. Tornadoes

10. Hurricanes Large, swirling, low pressure system that forms over the Atlantic Ocean. Must have winds of at least 119 km/h. Category 1-5 (250 km/h) Typhoon- forms over the Pacific Ocean. Cyclones- Form over the Indian Ocean.

11. Hurricanes

12. Images from Space

13. Strongest Hurricanes Begin as low pressure systems west of Africa. Steered by surface winds. travel west. Gains strength from heat + moisture of warm ocean water. When it hits land, it loses power and dumps water. Strongest winds are within 80 km of the eye. (50 miles)

14. Blizzards Winds at 56 km/h Blowing snow Visibility less than 400m These conditions must persist for 3 hours or more.

15. Blizzards

16. National Weather Service watch- conditions are favorable warning- weather exist, take cover!