Transcript Weather 2
II. Severe Weather A. Thunderstorms 1. Form at a cold front- warm air is pushed upwards by cold, dense air. 2. Warm, moist air rises higher in the atmosphere and condenses into clouds 3. Cumulonimbus clouds form; rain droplets get carried up and down through the cloud by winds, and fall as heavy rain. 4. Thunderstorms may bring heavy rains, hail, sometimes snow, and thunder and lightning! They don’t usually last for very long. (half an hour) 5. Lightning- when different parts of a cloud build up opposite charges, electricity flows between them. This is lightning! a) when a charge builds up in a cloud, it may discharge to the ground http://www.ultraslo.com/page/368032211 6. Thunder- occurs when lightning heats the air (over 30,000 degrees F). a)air expands quickly, then it cools very quickly and contracts b) Rapid movement of molecules forms sound waves B. Tornadoes 1. When a severe thunderstorm occurs (winds over 89 km/h), a tornado may result 2. A tornado is a violently rotating column or air that contacts the ground 3. Can rip apart buildings, uproot trees, lift up cars, and cause major damage and harm. 4. Tornadoes are measured on the Fujita Scale. It ranks tornadoes by how much damage they cause. C. Hurricanes 1. A large, swirling lowpressure system that forms over a warm ocean 2. Also called typhoons or cyclones, they must have winds of 119 km/h to be a hurricane. 3. Hurricanes start as low-pressure storms, then gain power from the moisture and warmth of ocean water 4. They travel west towards North America, gaining power as they come 5. When they hit land, they lose the warm moisture from the ocean, and begin to die out. 6. High winds and flooding can cause lots of damage. 7. High winds hitting the water cause the ocean to bulge upwards (storm surge) Q: Since hurricanes need warm water to grow stronger, during which seasons would you likely see hurricanes? A: Summer and Autumn (Fall) 8. Saffir-Simpson Scale- classifies hurricanes based on their wind speed and storm surges. a) tries to predict possible damages Identify some patterns you can see in this data table. D. Blizzards 1. Blizzards have a few criteria: a) low-temperature b) high winds (more than 56 km/h or 35 miles per hour) c) visibility less than 400 m d) falling or blowing snow e) Lasts for 3 or more hours E. Floods 1. When water covers the ground due to heavy rain, an overflowing lake, or an overflowing river 2. Sometimes the ground can’t soak up water fast enough 3. If the ground isn’t permeable, water can’t soak in, making floods 4. Concrete, blacktop, and other manmade surfaces don’t let water sink into the ground. http://www.uky.edu/AS/Geology /howell/goodies/elearning/mod ule12swf.swf F. Severe Weather Safety 1. Watch- conditions are favorable for severe weather (tornadoes, thunderstorms, floods, blizzards, hurricanes). Stay tuned for more info. 2. Warning- a severe weather condition already exists. Take immediate action! During a tornado or thunderstorm warning: Take shelter in the basement, or middle of the building away from windows. Hurricane or flood Warning: Be prepared to leave, move inland to higher ground For a Blizzard warning, STAY INDOORS! Being outside too long can give you frostbite, and you can get lost in the blinding snow!