1. Weather and Climate Part 3 - Violent Storms CGF3M Crescent School Text source: http://weathereye.kgan.com

2. Hurricanes Thunder and Lightning Hail Storms Tornadoes Winter Precipitation

3. HURRICANES There is a separate slide show dealing with Hurricanes in more detail

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12. What is a storm surge:

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18. THUNDER AND LIGHTNING AND HAIL

20. How Lightning is created: In storm clouds, tiny particles in the cloud move around picking up positive or negative energy charges, like when shoes scuff a rug. The positive charged particles stay light, and rise to the top of the cloud. The negative charged particles get heavier, and collect at the bottom of the cloud. As more particles become charged, they divide into opposing groups in the cloud. When the power of attraction between them gets too great, the particles discharge their energy at each other, completing a path for electricity to travel through the air. We call this flow of electricity lightning.

21. It's the negative charges in the bottom of the cloud that cause lightning to strike the ground. When the negatively charged particles group together, they begin to seek out positive charges from the ground below. The excess electrons create a channel of charged air called a leader that reaches down to the ground below. The leaders attract other charged ground-based channels called streamers.

22. How Thunder is created: The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels at 186,000 miles in a second, almost a million times the speed of sound. Sound travels at the slower speed of one-fifth of a mile in the same time. So the flash of lightning is seen before thunder is heard. By counting the seconds between the flash and the thunder and dividing by 5, you can estimate your distance from the strike (in miles).

23. But why does lightning cause thunder at the same time it strikes? Lightning causes thunder because a strike of lightning is incredibly hot. A typical bolt of lightning can immediately heat the air to between 15,000 to 60,000 degrees Fahrenheit. That's hotter than the surface of the sun! A lightning strike can heat the air in a fraction of a second. When air is heated that quickly, it expands violently and then contracts, like an explosion that happens in the blink of an eye. It's that explosion of air that creates sound waves, which we hear and call thunder.

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26. How does Hail form? Hail is created when small water droplets are caught in the updraft of a thunderstorm. These water droplets are lifted higher and higher into the atmosphere until they freeze into ice. Once they become so heavy they will start to fall. It all depends on the storms strength. If the smaller hail stones get caught in the updraft again they get more water on them. They get lifted again freeze and fall. This happens over and over until the hailstone is too heavy, and then falls.

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32. TORNADOES

33. Tornado conditions are caused when different temperatures and humidity meet to form thunderclouds. In the United States, warm, wet winds from the Gulf of Mexico move northward in spring and summer, meeting colder, dry Canadian winds moving southward. The place where these two winds meet is called a dry line.

34. High, dry air coming from the north piles on top of low-moving, moist Gulf air at a height of over 10,000 feet. The warm southern winds try to rise, but the cold northern air blocks them. This clash causes the warm, trapped air to rotate horizontally between the two air masses.

35. At the same time, the sun heats the earth below, warming more air that continues to try and rise. Finally, the rising warm wind become strong enough to force itself up through the colder air layer. When this occurs, the cold air on top begins to sink, sending the rising warm wind spinning upward.

36. The warm winds rotate faster and faster in a high column. When the updraft is strong, the column can rise to heights of 10 miles or more, twisting at speeds of up to 100 miles an hour. The rotating winds produce strong storm clouds about 70,000 feet high, sometimes spreading 10 miles wide.

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41. Click here to see an interesting animated example of how a Tornado forms: http://news.bbc.co.uk/2/hi/5328524.stm Check out the one for Hurricanes as well.

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51. Flash Corner: Tornadoes Hurricanes

52. THE END