Download Unit Study Guide on Thunderstorms, Tornadoes, and Hurricanes.

Severe Weather
Tornadoes
Tornadoes
What is a Tornado?
• A tornado is a violently rotating column of
air extending between, and in contact with,
a cloud and the surface of the earth
• Tornadoes can come one at a time or in
clusters
• They can also vary in size, length, width,
direction of travel, and speed
• The occur during severe thunderstorms
– Supercell: Spin Thunderstorm Cloud
How Do You Measure a Tornado?
• Since February 1, 2008 tornadoes have
been measured based on the Enhanced
Fujita Scale (EF)
• This scale helps determine the speed of a
tornado from weakest to strongest
The Enhanced Fujita Scale
EF 0
EF 1
EF 2
EF 3
EF 4
EF 5
65 to 85 MPH
86 to 110 MPH
111 to 135 MPH
136 to 165 MPH
166 to 200 MPH
Over 200 MPH
When and Where Do Tornadoes
Occur?
• Tornadoes can occur in any state and any
time of year
• They typically occur from March to August
• The most common tornadoes are in
“Tornado Alley”
• “Tornado Alley” - Arkansas, Iowa, Kansas,
Louisiana, Minnesota, North Dakota, Ohio,
Oklahoma, South Dakota, and Texas
Important Terms for Tornadoes
• Tornado Watch: weather conditions are
likely for tornadoes to form in our area
• Tornado Warning: A tornado has been
sighted in our area
Tornado Safety Tips
• Seek shelter immediately when a tornado
warning is issued
– Underground shelter is best
– If not available, find an inside room, hallway,
or closet on the lowest floor and away from
windows
• Listen to the radio or watch TV for updates
on the storm
Hurricanes
What is a Hurricane?
• A hurricane is an intense tropical weather
system that has a well-defined circulation
and sustained winds of 74 MPH or higher
• Coriolis Effect
– Northern Hemisphere: Spin Counterclockwise
– Southern Hemisphere: Spin Clockwise
How Do Hurricanes Form?
• They form when they gather heat and
energy through contact with warm ocean
waters
• Water evaporates from the water and the
moisture produces a storm
• They can also form when a wind pattern
occurs near the surface of the ocean and
spirals inward
Storms Associated with Hurricanes
• Tropical Depression
– An organized of clouds and thunderstorms at
low level circulation with winds at a maximum
of 39 mph
• Tropical Storm
– An organized system of strong thunderstorms
with winds between 39 to 73 mph
When and Where Do Hurricanes
Occur?
• Hurricanes can occur during any time of the year
• Hurricane season is from June 1st to November
30th
• They can form in the Atlantic Ocean, Caribbean
Sea, Gulf of Mexico, and in the eastern Pacific
Ocean
How Do You Measure a Hurricane?
• Hurricanes are measured by their speed and it is
split into categories
• The categories range from one to five, with one
being the weakest and five being the strongest
• The classification of hurricane systems is called
the Safir-Simpson Hurricane Scale
Safir-Simpson Hurricane Scale
Category One
Category Two
Category Three
Category Four
Category Five
74 to 95 MPH
96 to 110 MPH
111 to 130 MPH
131 to 155 MPH
Winds greater then 155
MPH
Note: Hurricanes of Category Three or above are considered major
hurricanes.
Why Do Hurricanes Have Names?
• Hurricanes are named to help identify and keep
track of storms as they move across the ocean
• Atlantic hurricanes might have Spanish, French,
or English names since they come in contact
with the borders
• Hurricanes are named alphabetically by the
National Weather Service
Why Do Hurricanes Have Names? (2/2)
• In 1953, the National Weather Service began
using female names
• In 1979, they began to use both men and
women’s names
Important Hurricane Terms
• A Hurricane Watch occurs when a
hurricane is possible within 36 hours
– The storm is being tracked to predict where it
may hit
• A Hurricane Warning is issued when it the
storm is expected to hit within 24 hours
– Evacuation may be needed
Hurricane Safety Tips
• Know if the location you are in is a safe zone or
whether evacuation may be needed
• Protect windows and glass with plywood
• Turn off utilities
• Have a supply kit including first aid, water,
canned goods, battery powered radio, blankets,
etc.
• After evacuation, do not return until it has been
declared safe
Thunderstorms
What Makes a Thunderstorm?
• Moisture: cloud formation & rain
• Unstable air: relatively warm air rises rapidly
• Lifting: from sea breezes and mountain
interaction
Three Types of Thunderstorms
• Air Mass
– Result of localized convection in an unstable
air mass
• Frontal
– Form right along or just ahead of a cold front
• Orographic
– This type of storm is the result of air that is
forced upward by a mountain
Thunderstorm Facts
• Every thunderstorm produces lightning
– Lightning: Electrical discharge formed in
clouds during thunderstorms
• Heavy rain can lead to flash flooding
• Strong winds, hail, and tornadoes may be
associated with thunderstorms
Important Terms for Thunderstorms
• A Severe Thunderstorm Watch can be
issued by the National Weather Service
station
– This type of storm has winds of at least 58
mph or hail at least ¾ inch in diameter
• A Severe Thunderstorm Warning is issued
when a severe thunderstorm has actually
been observed
Thunderstorm Safety Tips
• Go inside and stay away from windows,
doors, and porches
• Stay away from trees and out of boats
• Avoid plumbing fixtures and contact with
electrical fixtures
• Stay off the phone!