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Severe Storms. 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. Thunderstorms. Lightning.
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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.
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.
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 moleculesforms sound waves heard as thunder.
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.
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.
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)
Blizzards • Winds at 56 km/h • Blowing snow • Visibility less than 400m • These conditions must persist for 3 hours or more.
National Weather Service • watch- conditions are favorable • warning- weather exist, take cover!