SEVERE WEATHER
THUNDERSTORMS &
LIGHTNING
Thunderstorm Development
 Thunderstorms need:
 moisture
 warm air
 lifting capability (fronts, sea breeze, mountains)
 Cumulus clouds (white, puffy) form from lifting air and
develop into cumulonimbus clouds
Lightning
 Results from buildup and discharge of electrical energy between +
and – areas within a rising cloud
 Lightning rapidly heats the surrounding air, causing a shock wave
we hear as thunder
 Three types:
 Within cloud
 Between cloud
 Cloud-to-ground
Thunderstorm Formation
Lightning Formation
HURRICANES
Hurricane Life Cycle
• Start as pre-existing low pressure
systems, called tropical waves, over
warm ocean waters
• Evaporating ocean waters and
heated air rise and develop
thunderstorms
• Storms begin to swirl around the low
pressure center due to the Coriolis
Effect (spinning of the Earth)
Hurricane Structure
 Eye – sinking air in the center
of the storm forms a calm,
cloud-free eye that can be 20
– 40 miles across
 Eyewall – dense
thunderstorms surrounding
the eye; strongest winds
 Rainbands – thunderstorms
and clouds that spiral outward
from the center; spin counter-
clockwise in the northern
hemisphere
Hurricane Stages
 Tropical Depression – strengthening tropical wave;
winds less than 34 mph
 Tropical Storm – continued strengthening; winds
between 35 – 73 mph; named
 Hurricane – when winds reach 74 mph; eye forms
 Hurricanes lose energy when they make landfall, or
emerge into colder waters
Notice how
this
hurricane
got worse
over the
dark red
(warmer
water) and
finally died
when it got
over the
colder
water.
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 SafirSimpson 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.
A storm surge is the change in sea
level produced by wind pushing the
water up onto the shore. It is the
MOST damaging part of a hurricane.
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
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
Tornado Formation
 Changing wind direction and increased wind speed
prior to a thunderstorm creates an invisible, horizontal
spinning effect in the lower atmosphere
 Rising warm air within the thunderstorm tilts the
spinning air upward into the storm
 The vertical spinning column of air begins to rotate the
thunderstorm, and a tornado soon forms
Formation
Waterspout
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
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
Tornado Facts
 Waterspouts – tornadoes that form over water; usually
weaker than land tornadoes
 Tornadoes can be transparent, and only appear when
dust and debris get picked up into the funnel
 Tornadoes can occur anywhere on Earth, but are most
common in “Tornado Alley” in the central United States
Tornado Safety
 Tornado Watch – conditions are right for tornado
development
 Tornado Warning – one has been sighted or indicated in
the area; take shelter
 If inside – stay away from windows, get in a central
room or basement
 If outside – seek shelter, get out of cars and get on the
ground or in a ditch
More Severe Weather
 Flash Floods
 Heavy rainfall over a short
period of time; causes most
fatalities during thunderstorms
 Hail
 Strong vertical winds within
thunderstorm clouds (updrafts)
carry rain drops to heights
where they freeze; once they
get too heavy they fall to the
ground
SUN SAFETY
• The Sun’s ultraviolet radiation can cause health
risks, including skin cancer
• Surfaces like snow, water, and beach sand can
double the effect of UV radiation
HOW TO PROTECT YOURSELF