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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.
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.
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.
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.
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.
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
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)
4. Heat Lightning- The glow of lightning so far
away, the thunder can not be
heard.
D. Things to Avoid:
1. Phones
2. TV
3.
4.
5.
6.
Taking Showers
Trees
Swimming Pools
Athletic Events (Ex. Golf, Baseball, etc.)
“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.
4. This is when the funnel cloud starts to appear.
5. When it reaches Earth’s 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.)
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.
D. Tornado Classification:
1. We use the Fujita Scale to classify tornadoes.
F0
< 72 mph winds
F1
72-112 mph winds
F2
113-157 mph winds
F3
158-206 mph winds
F4
207-260 mph winds
F5
> 260 mph winds
2. Winds can’t be measured.
3. Damage is assessed to find the wind speeds.
II. Hurricanes:
A. What is a Hurricane?
1. A Hurricane is a very intense tropical lowpressure 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.
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.
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.
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.
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
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.
Retired Names Since 1986
Retired
Name
Replacement
Name
Allison
Andrea
Floyd
Franklin
Georges
Gaston
Iris
Ingrid
Keith
Kirk
Lenny
Lee
Michelle
Melissa
 katrina
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.)
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.
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.