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Severe Weather

Severe Weather. Solar Heating and Latitude. Solar Heating and the Seasons. Relationship of sun angle and solar radiation received on Earth. Air at high elevations: Cooler Expands Water vapor tends to condense. Air at sea level: Warmer More compressed Can hold more water vapor.

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Severe Weather

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  1. Severe Weather

  2. Solar Heating and Latitude

  3. Solar Heating and the Seasons

  4. Relationship of sun angle and solar radiation received on Earth

  5. Air at high elevations: Cooler Expands Water vapor tends to condense Air at sea level: Warmer More compressed Can hold more water vapor Solar Heating and Atmospheric Circulation

  6. Air Circulation & Convection Currents

  7. Coriolis Force

  8. Atmospheric Circulation & Convection Cells

  9. Air masses are classified on the basis of their source region

  10. Fronts • Types of fronts • Warm front • Warm air replaces cooler air • Shown on a map by a line with semicircles • Small slope (1:200) • Clouds become lower as the front nears • Slow rate of advance • Light-to-moderate precipitation

  11. Fronts • Types of fronts • Cold front • Cold air replaces warm air • Shown on a map by a line with triangles • Twice as steep (1:100) as warm fronts • Advances faster than a warm front • Associated weather is more violent than a warm front

  12. Cold Fronts and Warm Fronts

  13. Rotating Air Bodies • Bends in the polar jet create troughs and ridges • Forms cyclones and anticyclones

  14. Low Pressure Zone Formation Warm air rises Creates a low pressure zone At the Earth’s surface, air “feeds” the low pressure zone, moves counterclockwise High Pressure Zone Formation Cool air sinks Creates a high pressure zone At the Earth’s surface, winds blow clockwise Rotating Air Bodies

  15. Cyclones and Anticyclones

  16. Types of Severe Weather • Thunderstorms • Snow / Rain storms • Mid-latitude cyclones • Blizzards • Tornadoes • Tropical cyclones • Typhoons in the western Pacific • Cyclones in the Indian Ocean • Hurricanes in the U.S.

  17. Stages in the development of a thunderstorm

  18. Thunderstorms • How Lightning Works

  19. Thunderstorms

  20. Lightning Varieties cloud-to-ground Cloud discharge Ball lightning Blue jets Red sprites Elves (NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)

  21. Lightning Varieties Volcanic Lightning Nuclear Lightning Triggered Lightning (NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)

  22. Thunderstorms • Lightning - Don’t Get Struck! • Boating or swimming – get away from the water. • Try to take shelter in: • substantial, permanent, enclosed structures. • a car, truck or other hard-topped vehicle. • an area protected by a low clump of trees. • No shelter available? • Find a low-lying, open place away from trees, poles/metal objects and water. • Make yourself the smallest target possible. • Do not lie flat, as this makes you a larger target.

  23. Severe weather types • Tornadoes • How a Tornado Forms • Moist air from Gulf of Mexico • Fast moving cold, dry air mass from Canada • Jet stream moving east at 150 mph • Sets up shearing conditions

  24. Severe weather types • Tornadoes • How a Tornado Forms • Warm moist Gulf air releases latent heat, creates strong updraft • Updraft sheared by polar air, then twisted in a different direction by jet stream

  25. Severe weather types • Tornadoes • Why do some thunderstorms spawn tornadoes while others do not? • Super Cell Thunderstorms

  26. Severe weather types • Tornadoes • The Fujita-Pearson Scale • The size of a tornado is not necessarily an indication of its intensity!

  27. Tornadoes • “Tornado Capitol of the World” • CNN’s “10 deadliest U.S. tornadoes” Source: cnn.com

  28. Tornadoes • Tri-State Tornado, 18 March 1925 • Largest tornado known • Travelled 353 km (219 mi) across Missouri, Illinois and Indiana • Widest swath recorded - 1 mi in diameter • Devastated 23 cities • Killed 695 people and injured 2,027 In this photo, engineers examine a board that the tornado's high-speed winds drove through a larger plank. cnn.com

  29. Tornadoes • The Super Outbreak, 3-4 April 1974 • 5 weather systems collided • Dry air from the SW overrode moist Gulf air, creating an inversion layer • Gulf air pushed through the inversion layer • Thunderstorms developed

  30. Tornadoes • The Super Outbreak, 3-4 April 1974 • 147 tornadoes • 6 F5 tornadoes • 13 states • 16 hours

  31. Tornadoes • Why don’t tornadoes strike large cities? • Occur over large regions • Cities are relatively small targets • Oklahoma City Tornado (1999)

  32. Tornadoes • Safe Rooms • Best ones are underground • Some are above ground

  33. Mid-latitude Cyclones • Idealized weather • Middle-latitude cyclones move eastward across the United States • First signs of their approach are in the western sky • Require two to four days to pass over a region • Largest weather contrasts occur in the spring

  34. Mid-latitude Cyclones

  35. Mid-latitude Cyclones • Nor’easters • The Eastern U.S. “White Hurricane” of 1993 • AKA “Storm of the Century” • Three storm fronts all converged with a trough in the jet stream • Collision began in Florida, and moved up the eastern seaboard with the jet stream • 238 people died from Cuba to Canada • 48 sailors lost at sea

  36. X 1. Low pressure zone from Gulf of Mexico – lots of thunderstorms 2. Trough in jet stream drew in fast-moving arctic front 3. Trough also drew in a rain/snow front from the Pacific 2 1 3

  37. Mid-latitude Cyclones • Blizzards • Form when a long cyclone brings • Cold 60 km/hr winds • Freezing temperatures • Lots of snow • Can travel very slowly • Storm itself usually doesn’t kill • Shoveling snow, auto accidents, etc.

  38. Mid-latitude Cyclones • Blizzards • Northeastern United States, 6-8 January 1996 • Storm centered on Ohio, Pennsylvania, West Virginia, and New Jersey • 50 mph winds, record snow falls • 154 people died • Warm, wet weather immediately followed • 187 people died

  39. Mid-latitude Cyclones • Ice Storms • Formation: • Falling snow and ice melt, change to rain, then freeze again as they reach the ground • Sleet • Freezing rain

  40. Mid-latitude Cyclones • Ice Storms • Canadian Ice Storm, 5-9 January 1998 • 80 hours of freezing rain • Power systems collapsed • had to be completely replaced • People without power for up to 4 weeks • 16 U.S. and 28 Canadian deaths • Damages • $1.4 billion for the U.S. • $3 billion for Canada Source: cnn.com

  41. Hurricanes

  42. Hurricanes • Only natural disaster that is given a human name • Actually large tropical cyclones • Convert heat in the ocean into winds • Exports excess heat from the tropics to the midlatitudes

  43. Hurricanes • How a Hurricane Works • Tropical disturbance • Low pressure zone develops and draws in clusters of thunderstorms and winds

  44. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Surface winds strengthen, move about the center of the storm • Central core funnels warm moist air up towards stratosphere • Air cools, vapor condenses, latent heat released • Fuels more updrafts, cycle repeats, storm grows

  45. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Storm has sustained surface wind speeds of +39 mph

  46. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Hurricane • Surface winds consistently over 74 mph

  47. Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Hurricane • The Eye • As wind speed increases, winds are spiraled upwards prior to reaching the center • A distinctive clear “eye” is formed • Strongest winds are located on the walls of the eye

  48. Hurricane Wind Patterns

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