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Severe Weather

Explore the classification of air masses, their impact on weather conditions, and various severe weather types like tornadoes and hurricanes.

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Severe Weather

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  1. Severe Weather

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

  3. Air masses and weather • Continental polar (cP) • From northern Canada and interior of Alaska • Winter – brings cold, dry air • Summer – brings cool relief • Responsible for lake-effect snows • cP air mass crosses the Great Lakes • Air picks up moisture from the lakes • Snow occurs on the leeward shores of the lakes

  4. Air masses and weather • Maritime tropical (mT) • From the Gulf of Mexico and the Atlantic Ocean • Warm, moist, unstable air • Brings precipitation to the eastern United States

  5. Air masses and weather • Continental tropical (cT) • Southwest and Mexico • Hot, dry • Seldom important outside the source region

  6. Air masses and weather • Maritime polar (mP) • Brings precipitation to the western mountains • Occasional influence in the northeastern United States causes the "Northeaster" in New England with its cold temperatures and snow

  7. 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

  8. Warm Front / High pressure system Cold Front / Low pressure system Rain!

  9. 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 • Weather behind the front is dominated by • Cold air mass • Subsiding air • Clearing conditions

  10. Cold Front / Low pressure system Warm Front / High pressure system Rain/Snow Thunderstorms

  11. Fronts • Types of fronts • Stationary front • Flow of air on both sides of the front is almost parallel to the line of the front • Surface position of the front does not move • Occluded front • Active cold front overtakes a warm front • Cold air wedges the warm air upward • Weather is often complex • Precipitation is associated with warm air being forced aloft

  12. Middle-latitude cyclone • Primary weather producer in the middle-latitudes

  13. Middle-latitude cyclone • 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

  14. Cloud patterns typically associated with a mature middle-latitude cyclone

  15. Stages in the development of a thunderstorm

  16. Severe weather types • Tornadoes • A rapidly spinning column of air descending from a large thunderstorm • Have the highest wind speeds of any other weather phenomenon. • In the U.S., tornadoes move northeast at speeds up to 100 km/hr (62 mph) • Rotating wind speeds sometimes in excess of 500 km/hr (310 mph)

  17. 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

  18. 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

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

  20. Severe weather types • Tornadoes • Scales • The Fujita-Pearson Scale measures wind speed • The size of a tornado is not necessarily an indication of its intensity • Large tornadoes can be weak, and small tornadoes can be violent

  21. Severe weather types • 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

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

  23. Severe weather types • 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

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

  25. Severe weather types • Hurricanes • How a Hurricane Works • Tropical disturbance • Tropical depression • Tropical Storm • Hurricane • Surface winds consistently over 74 mph

  26. Severe weather types • 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

  27. Hurricane Origins • Form in the tropics ~ 5° and 20 ° latitude • Cannot form at the equator (Coriolis effect = 0)

  28. Hurricanes • Hurricane Damages • Storm Surges • Large mound of water builds up beneath the eye • Reaches land as a surge of water

  29. Hurricanes • Hurricane Damages • Storm Surges • Wind speed varies depending upon which side of the hurricane you’re on • Amount of damage on the coastline will vary accordingly

  30. Hurricanes • Hurricane Damages • Heavy Rains • Mudflows and Debris Avalanches • Flooding

  31. ~ End ~

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