Download Severe Weather 21.2- page 578-582 Standard 912.E.7.6 – Relate

Severe Weather
21.2- page 578-582
Standard 912.E.7.6 – Relate unequal heating of land and water to form global wind systems
and weather events such as tornadoes and thunderstorms.
Use this information and your book to
create your foldable organizer about
severe storms
Relate the formation of severe weather to specific physical factors including: temperature,
humidity, air pressure and wind speed
Describe the lifecycle of a thunderstorm
Thunderstorms
Thunderstorms need three things:
When?
Thunder and Lightning
Thunderstorm safety
Tornadoes
Tornado Formation
Tornado Damage
Enhanced Fujita Scale
EF0-EF5
Tornado Alley
Describe the stage in the development of a hurricane
 Storm with lightning and thunder.
 Produced by a cumulonimbus cloud
 Can have gusty winds, heavy rain and sometimes hail.
 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.
 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.
 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.
 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!
 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!
 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.
 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.
 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
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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
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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
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.
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.
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See separate chart
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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.
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.
 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.
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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!