Severe Weather
16.3- page 496 / Name:
Use this information to create your foldable organizer about severe storms / Standard:S6E4b–Relate unequal heating of land and water to form global wind systems and weather events such as tornadoes and thunderstorms.
Period:
Date
Notes
What are the differences in the types of severe weather? How are they similar?
Thunderstorms /
  • Storm with lightning and thunder.
  • Produced by a cumulonimbus cloud
  • Can have gusty winds, heavy rain and sometimes hail.

  • Thunderstorms need three things:
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  • Moisture - to form clouds and rain.
  • Unstable Air - relatively warm air that can rise rapidly.
  • Lift - fronts, sea breezes and mountains can lift the air up higher, to help form thunderstorms.

When? /
  • Most likely to occur in the spring and summer months and during the afternoon and evening hours.
  • Can occur year-round and at all hours of the day or night.
  • Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon.
  • Thunderstorms often occur in the late afternoon and at night in the Plains states.

Thunder and Lightning /
  • Has a sibling rubbed their feet across carpet and then touched you? If so, then you know that you can get shocked by static electricity.
  • Lightning works in the same way.
  • Lightning a big electrical discharge between clouds and or the ground.
  • Thunder is the sound lightning makes.
  • Sound travels about 1 mile in 5 seconds.

Thunderstorm safety /
  • Severe Thunderstorm Watch -conditions are conducive to the development of severe thunderstorms in and close to the watch area.
  • Severe Thunderstorm Warning - a severe thunderstorm has actually been observed by spotters or indicated on radar, and is occurring or imminent in the warning area
  • Time to take cover!

Tornadoes /
  • Rapidly rotating, funnel shaped cloud.
  • Most locally destructive of all storms.
  • Usually touch the ground for only a few minutes.
  • Wind speeds can be over 200mph!

Tornado Formation
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  • Develop in thunderstorms in cumulonimbus clouds.
  • How the column of air begins to rotate is not completely understood by scientists.
  • Rotation appears to happen when winds at two different altitudes blow at two different speeds creating wind shear.
  • This causes a horizontal rotation
  • If this column gets caught in a supercell updraft, the updraft tightens the spin and it speeds up
  • (much like a skater's spins faster when arms are pulled close to the body.)
  • A funnel cloud is created.

Tornado Damage
Enhanced Fujita Scale
EF0-EF5 /
  • Tornadoes are usually less than a 100 yards wide.
  • The damage they inflict is severe but very localized.
  • The Enhanced Fujita scale uses the damage to estimate the wind speed.
  • The more severe, the less common.
  • EF-5’s are the strongest, most damaging tornadoes.

Tornado Alley /
  • The area over which tornadoes occur most often in North America is called Tornado Alley.
  • It covers the Great Plains which is between the Rocky Mountains and the Appalachian Mountains. It includes all or half of the 13 mid-west states.

Tornado Safety /
  • Tornado Watch: conditions are favorable for tornadoes.
  • Tornado Warning: Tornado has been sighted. Take cover if it is in your area.
  • Basements are the best place if there is a tornado.

Hurricanes /
  • A tropical cyclone that occurs in the Atlantic.
  • Starts as a tropical depression (winds less than 39mi/hr).
  • Becomes a tropical storm and is given a name when the winds exceed 39mi/hr.
  • Finally becomes a hurricane when the winds reach 74mi/hr.
  • Called typhoons in the Pacific/cyclones in the Indian Oceans

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  • Form in warm, tropical waters.
  • Water must be at least 80°F(27°C).
  • Needs warm, moist air and converging winds.
  • Has a large difference in air pressure.
  • Formed by the heat energy and as long as the water is warm are self-sustaining.
  • The moist, warm air circulates around a well defined center.
  • The lower the pressure at the center, the faster the winds will rush in to try to fill it.

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  • Eye: center of the hurricane. Weather is calm, may be clear, and will have no rain.
  • Winds will come from the opposite direction after the eye passes.
  • Eye wall: the vertical wall of clouds that surround the eye. Will have the most intense winds and rainfall.
  • Rain bands will move counter-clockwise around the eye. These bands with hurricane force winds can extend over 300 kilometers from the eye. So the storms can affect a wide area.

  • Hurricanes are steered by the global winds.
  • So the storms in the tropics are steered to the west by the trade winds. When they get far enough north the westerlies take over and steer them east.
  • Once over land (or cold water), they lose strength as they no longer have a source of warm water to draw energy from.
  • Friction with the land can slow the winds down also.

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  • The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity (wind speed).
  • This scale uses wind speed to estimate damage due to high winds and flooding
  • Called Categories (Katrina was a Category 5 hurricane.)

  • Hurricane can cause enormous damage when they come ashore.
  • While high winds do a lot of damage, flooding is more serious.
  • Heavy rains cause flooding, especially if the hurricane is slow moving.
  • Storm surge is even more serious. It is a dome of water caused by low pressure and high winds. If it coincides with the high tide, many coastal areas will be devastated.

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  • Since at least 1945, the US Navy and later the Air Force started naming tropical cyclones.
  • At first they used exclusively English female names, but since 1978 have started to alternate male and female names (alphabetically).
  • Different areas of the world tend to use local names for their areas.
  • There is a six year list.
  • If they run out of names in a year they use the Greek alphabet.
  • Hurricanes that do significant damage will have their name retired.

  • HURRICANE WATCH - Hurricane conditions with sustained winds of 74 mph or greater are possible in your area within the next 36 hours. Time to think about evacuating!
  • HURRICANE WARNING - Hurricane conditions are expected in your area within 24 hours. Past time to evacuate!