Ch.13 – The Nature of Storms Thunderstorms • Thunderstorms • Violent disturbances in the atmosphere, which involve sudden changes in air pressure. • Heavy rain storms with thunder and lightning. • Form in cumulonimbus clouds, or thunderheads. • Form when warm air is forced upward by a cold front, or during the afternoon when the air is hot and humid. • How thunderstorms form… 3 ways. • Moisture • Lifting • Stability • Limits… are the same. Thunderstorms • Types of Thunderstorms • Air-Mass • Frontal • Thunderstorm development… 3 Stages • Cumulus stage • Mature Stage • Dissipation Stage Thunderstorms • What causes lightning? • Electrical discharge between clouds or the ground. • What causes thunder? • Super heating of the air around lightning causes rapid expansion and an explosion. • Safety • Get inside! • Stay away from metal, tall structures, wide open spaces and get off of bodies of water. • When inside, avoid using phones, electrical appliances, and plumbing fixtures. • Cars are safe, but stay inside and don’t touch metal. Severe Weather • Main characteristics of thunderstorms. • Wind • Rain • Lightning • Weather Cells • Supercells • Rotating updrafts. • 150 mph winds. • Produce Tornadoes. • Downbursts • Straight downdrafts. • 150 mph winds. • Produce Micro & Macrobursts. Severe Weather • How does hail form? • Water droplets freeze inside a thunderhead. • Updrafts and down drafts exist side by side. • How does a tornado form? • A change in wind direction and speed creates horizontal rotation(like a rolling pin). • Updrafts tilt the rotating air into a vertical position. • Updrafts stretch the tornado and it spins faster. • Air is removed from the center, which drops air pressure inside, causing winds to increase. Severe Weather Severe Weather • Tornado Distribution in the U.S. • Most common in the Central U.S., due to large temperature contrasts. • Tornado Safety • Watches & Warnings • Watch means conditions are right, but no tornado…yet. • Warning means a tornado has been spotted. • Indoors- Get into the basement if possible, if no basement is available, find an area away from windows and doors. • Outdoors- Get inside! Or lie in a ditch, or low lying area. Tropical Storms • Tropical Cyclones • Hurricanes, Typhoons, & Cyclones… • Need two ingredients to form… • Lots of warm ocean water and lift. • Movement is toward the west, unpredictable, and slows as it approaches land. • Three stages of cyclone formation. • Formative • Mature • Dissipation Tropical Storms • Three main dangers of a Hurricane. • Damage • Winds • Storm Surge • Eye of the Hurricane • It is the center of a hurricane, an area of calm in the storm, but it is surrounded by the storms most powerful winds. • Safety • Evacuate! If you do stay, treat it like tornado safety. Tropical Storms Tropical Storms Recurrent Weather • Floods • Unexpected floods which occur when so much water pours into a stream that it overflows its banks and covers the land on either side of the channel. • Most are due to large amounts of rainfall in a short period of time. • Flood Safety • Predicting a flood… • Weather forecasting • Flood watches • In an emergency… • Get to higher ground • Evacuate • Hazards • Polluted water, mudslides, structural damage. Recurrent Weather • Droughts • Extended periods of below average rainfall. • Dust Bowl = the most famous U.S. • The result of persistent high pressure. • Heat & Cold Waves • Read pgs.362-365.