Transcript 20.3 Severe Storms

Severe Weather
Thunderstorm
 Storm that generates lightning and
thunder; often produces gusty
winds, heavy rain, hail
 From cumulonimbus cloud(s) along a
cold front
 Occurs all over the earth (most in
the tropics) when warm, humid air
rises in an unstable environment
Thunderstorm
time lapse
Stages in the Development
of a Thunderstorm
1:
2:
3:
Mature stage:
• Simultaneous updraft and downdraft create strong winds
• Raindrops merge and get bigger as they fall long distance
through cloud
Hail formation
• Balls of ice that
fall from a
cumulonimbus
cloud
• Ice gets swept up
and down in
updrafts inside
cloud
• Grow larger as
water refreezes
each time they rise
Largest Recorded Hailstone
Lightning
 During mature storm stage
 Updrafts and downdrafts rub against
each other, building up static
electricity
 Bottom becomes negatively charged;
ground is positively charged
 May occur within a cloud, between
clouds, or from cloud to ground
How Stuff
Works:
Lightning
Tornado
 Violently rotating column of air
touching earth and cumulonimbus cloud
 Most form during severe thunderstorms
Tornadoes
Video:
Tornado Crosses
Kansas Highway
Tornado Intensity
 Fujita Scale: rates
storm by damage
caused
 Tornado safety
 Watch: conditions
are right for a
tornado
 Warning: tornado
has been sighted
BBC Tornado
Animation
Hurricane
 Large areas of low pressure rotating
counter clockwise
 Central eye is an area of high pressure
 Season starts in June, peaks in Sept
 Favorable conditions:
 Unstable atmosphere
 Warm ocean temps
Other names: Typhoon (Pacific
Ocean), Willy-willy (Australia)
BBC Hurricane
Animation
Where Hurricanes Form
 7 Basins
New Orleans
Strong Side
Weak Side
Cross Section of a Hurricane
Eye = high-pressure center
Eyewall = circle of strong thunderstorms surrounding eye
Rainbands = arms formed by curved lines of storm clouds
Saffir-Simpson Hurricane Scale
Category
Animation
Hurricane Hazards
• Flying debris
• Tornadoes
• A storm surge is
water pushed toward
the shore by the
force of the winds
swirling around the
storm
• Severe flooding
• Beach erosion
• Causes more
damage than
winds