Transcript Extreme Weather power point

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A violently rotating column of air extending
from within a thundercloud down to ground
level
 Tornadoes vary in diameter from tens of
meters to nearly 2 kilometres, with an
average diameter of about 50 metres
 Most tornadoes in the northern hemisphere
create winds that blow counter-clockwise
around a center of extremely low
atmospheric pressure, while in the southern
hemisphere the winds generally blow
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Winds that are at their peak can have
speeds that range from near 120 km/h to
almost 500 km/h The forward motion of a
tornado can range from a near halt to almost
110 km/h
 A tornado becomes visible when a funnel
cloud forms in extreme low pressures, or
when the tornado lofts dust, dirt, and debris
upward from the ground.
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Here is a picture of a tornado that took place in central Oklahoma. This tornado is known
as a “multiple-vortex” tornado.
Many tornadoes, including the strongest
ones, form from a special kind of
thunderstorm known as a supercell (see
photo on next slide)
 A supercell is a long-lived, rotating
thunderstorm 10 to 16 km in diameter that
may last several hours, travel hundreds of
miles, and produce several tornadoes.
 There is a more thorough presentation on
formations at the end of the show
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Above is a picture of a supercell. This is what triggers a tornado.
Not many tornadoes occur in Canada
 America has the most tornado appearances
than any other country, with over 800 a year!
 In fact, in the U.S.A there is a region called
“Tornado Alley” which you will see a map of
on the following
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As you can see, not a lot of Tornadoes occur in Canada. Unfortunately the most
destructive ones strike in Southern Ontario, where we just happen to live.
This picture above is what has been nicknamed Tornado Valley (where area is mostly red)
Meteorologists can predict tornado
probability by for an area or along a line by
watching cold and warm fronts
 A jet stream lying above and to an angle to
the surface wind direction, plus a large
difference in water vapour in the air on the
two sides of a front are factors to consider
 By using a Doppler radar(see next slide)
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It measures the speed and direction of the movement of clouds, in addition to cloud
density. In this image of a thunderstorm over Oklahoma, Doppler radar shows a
mesocyclone, a rotating mass of air that may signal that the formation of a tornado is
forthcoming.
Shapiro, Alan. "Tornado." Microsoft®
Student 2008 [DVD]. Redmond, WA:
Microsoft Corporation, 2007.
 Cook, David. "Predicting Tornadoes."
Newton. 04 June 2008. Argonne National
Laboratory. 04 June 2008
<http://www.newton.dep.anl.gov>.
 Tornado." Wikipedia. 05 June 2008. 03 June
2008 <http://en.wikipedia.org/>.
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Please do not talk during these videos 
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Canada Video:
http://archives.cbc.ca/environment/extreme_w
eather/topics/1713/
 Formation Slideshow:
http://encarta.msn.com/media_701878950_76
1554892_-1_1/Tornado!.html
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