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Severe Weather
I. Severe Weather Storms

A. Thunderstorms

1. Thunder Storms occur when warm, moist air
moves upward rapidly, cools, condenses
and forms cumulonimbus clouds.
2. These clouds are formed from strong updrafts
caused by rapidly rising air.
3. As water drops become to heavy, they start to
fall toward the ground.
4. The falling water causes strong downdrafts of
wind.
5. The rapid updrafts downdrafts build up
electrical charges in the clouds.
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• 6. Some charges are positive and negative
• 7. When current flows between regions of opposite
  electrical charges, lightning flashes.

8. The resulting sound wave is thunder.
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B. What causes thunder and lightning?
1. Opposite charges attract.
2. Like charges repel.
3. Negatively charged bottom of Cb cloud
attracts positively charged area or objects on
the ground, as the attraction builds a
connection can be made and the current will
flow.
4. This is a lightning bolt.
5. Thunder results from the rapid heating of the
air around the lightning bolt.
6. Lightning can reach temperatures of 30,000
degrees C.
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7. This extreme heat causes the air around
lightning to expand rapidly.
8. After the lightning is gone the air cools and
contracts.
9. This rapid motion of air particles cause
sound waves called thunder.
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C. Facts about thunder lightning
1. Lightning travels at the speed of light, so
it is seen almost instantly. (300,000 km/s,
186,000 m/s)
2. Thunder travels at the speed of sound, so it
takes longer to hear it. (1000 ft/s)
a.) 1 mile approx. 5 seconds after lightning
you will hear the thunder.
b.) 1 km approx. 3 seconds after lightning
you will hear the thunder.
3. Causes an average of about 200 deaths per
year.
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Ball lightning is a natural phenomenon, or
debatably, a pseudoscientific theory. It is
sometimes associated with thunderstorms. It takes
the form of a long-lived, glowing, floating
object, as opposed to the short-lived arcing
between two points commonly associated with
lightning. An early attempt to explain ball
lightning was recorded by Nikola Tesla on March
5, 1904
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• Sheet lightning (heat lightning)
• is real lightning, it's just far away. A
  thunderstorm dozens of miles away only spreads
  its flashes of light, not it's thunder, wind or
  rain. It's called heat lightning because it is on
  hot nights that small storms can kick up a windy,
  rainy fuss in one town and leave neighboring
  towns just viewing this heat lightning. But right
  underneath the storm, the lightning is called --
  lightning -- and it can strikes a nearby tree
  with a tremendous clap of thunder. Miles away the
  same bolt is only seen as it back lights the side
  of a cloud
• (hence the name sheet lightning)

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The glow of lightning so far away, the thunder
can not be heard.
4. Heat Lightning-
D. Things to Avoid
1. Phones
2. TV
3. Taking Showers
4. Trees
5. Swimming Pools
6. Athletic Events (Ex. Golf, Baseball,
etc.)
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Severe Weather II
I. Tornadoes
A. What is a tornado?
1. It is a violent funnel shaped wind storm that
moves in a narrow path across land.
B. What causes tornadoes to form?
1. In very severe thunderstorms, the wind at
different heights, blow in different directions,
at different speeds.
2. Wind Shear-
the difference in wind direction and wind speed.
3. Strong updrafts tilt the wind shear and
produce rotation inside of the thunderstorm.
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4. This is when the funnel cloud starts to
appear.
5. When it reaches Earths surface, they are
called tornadoes.
C. Facts about tornadoes
1. Internal winds can reach up to 500 km/hr or
300 mph.
2. Paths of tornadoes are irregular. The path
can change at any time.
3. Width of a tornado can be from 100 meters
wide to 600 meters wide. (Largest are about ½ -1
mile wide.)
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4. Life span is usually less than one hour. (15
minutes on average)
5. Usually occur in the southwest corner of a low
pressure system.
Warm moist air and cold dry air meet and
form large thunderstorm cells.
6. 3 out of every 4 tornadoes in the world occur
in an area called Tornado Alley.
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D. Tornado Classification
1. We use the Fujita Scale to classify
tornadoes.
F0 lt 72 mph winds
F1 72-112 mph winds
F2 113-157 mph winds
F3 158-206 mph winds
F4 207-260 mph winds
F5 gt 260 mph winds
2. Winds cant be measured.
3. Damage is assessed to find the wind speeds.

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II. Hurricanes
A. What is a Hurricane?
1. A Hurricane is a very intense tropical
low- pressure system that has winds of 74 mph
(120km/hr) or more.
B. What causes the hurricane to form?
1. Wind from the southeast trade winds meet
winds form the northeast trade winds.
2. These winds start to spin counterclockwise.
3. A low-pressure system forms in the middle of
the spin
4. Air sinks in the center of this system.
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5. Outside of the center, warm moist air rises
and forms clouds.
6. The center of the hurricane is called the eye
of the storm. (high pressure)
7. Outside the eye is an area called the eye
wall. (low pressure, most intense area of the
storm)
8. When winds reach 74 mph, 120 km/h the storm
is called a hurricane.
C. Facts about hurricanes
1. They get their energy from the heat of the
water.
2. Hurricanes weaken when they reach land or
cold water.
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3. Wind speeds can reach 200 mph in the eye
wall.
4. Most damage is not done by high winds or
rain.
5. Storm Surge causes the most damage.
a.) can raise high tide 20-30 feet.
b.) Causes extensive flooding.
c.) Drowning deaths.
d.) Building damage.
D. Hurricane Names
1. Pre 1953 hurricanes were classified only by
date.
2. 1953-1979 only female names were used.
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3. 1979-present alternating male and female
names are used
4. Names are recycled every six years.
5. Names of the strongest storms are retired
from use.
6. A name is given to the storm after winds
reach 65 mph.
7. A group of people develop a list to use each
year.
8. The list is in alphabetical order. The first
storm name starts with A.
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Hurricane Names Selected for the Atlantic Basin
1997/2003 1998/2004 1999/2005 2000/2006 2001/2007 2002/2008
Ana Alex Arlene Alberto Allison Arthur
Bill Bonnie Bret Beryl Barry Bertha
Claudette Charley Cindy Chris Chantal Cesar
Danny Danielle Dennis Debby Dean Dolly
Erika Earl Emily Ernesto Erin Edouard
Fabian Frances Floyd Florence Felix Fran
Grace Georges Gert Gordon Gabrielle Gustav
Henri Hermine Harvey Helene Humberto Horrtense
Isabel Ivan Irene Isaac Iris Isidore
Juan Jeanne Jose Joyce Jerry Josephine
Kate Karl Katrina Keith Karen Kyle
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Larry Lisa Lenny Leslie Lorenzo Lili
Mindy Mitch Maria Michael Michelle Marco
Nicholas Nicole Nate Nadine Noel Nana
Odette Otto Ophelia Oscar Olga Omar
Peter Paula Phillippe Patty Pablo Paloma
Rose Richard Rita Rafael Rebekah Rene
Sam Shary Stan Sandy Sebastien Sally
Teresa Tomas Tammy Tony Tanya Teddy
Victor Virginie Vince Valerie Van Vicky
Wanda Walter Wilma William Wendy Wilfred
Hurricanes retired since 1985.
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Retired Names Since 1986
RetiredName ReplacementName
Allison Andrea
Floyd Franklin
Georges Gaston
Iris Ingrid
Keith Kirk
Lenny Lee
Michelle Melissa
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• katrina

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III. Blizzards
A. What is a blizzard?
1. A snow storm that meets all of the following
conditions is considered a blizzard.
a.) Wind speeds over 50 mph.
b.) Whiteout condition snow. (1/4 mile
visibility.)
c.) Below freezing temperatures. (27 F. or
lower.)
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IV. Severe Weather Watches Warnings
A. The National Weather Service only issues
watches and warnings.
B. What does a weather watch mean?
1. Means that severe weather is possible.
2. Be alert and listen for further reports.
3. Estimates of conditions are usually given.
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C. What does a weather warning mean?
1. Means that severe weather has been sighted,
detected in an area, or will be in an area soon.

2. Locations of the warning are given.
3. Direction of the storms should be given.
4. Probable conditions and intensity of the
severe weather will be given.
5. Evacuations may occur in the strongest
storms.