Transcript Thunderstorms

What is a thunderstorm?
• A storm resulting from strong rising air currents
accompanied by rain, thunder, and lightning
• The typical thunderstorm is 15 miles in diameter and last
an average of 30 minutes. Nearly 1,800 thunderstorms
are occurring at any moment around the world. That’s 16
million a year!
What does a thunderstorm need?
– Moisture
– Unstable air – usually warm air that can rise rapidly
– Lift – fronts, breezes, or mountains that help lift air
Formation – Stage 1
Developing Stage, also called Cumulus Stage
• cumulus cloud pushed upward by a rising
column of air called an updraft
• cumulus cloud continues to grow into a towering
cloud
• little to no rain during this stage but occasional
lightning
• lasts about 10 minutes
Developing stage seen here
Formation – Stage 2
• Mature Stage
– The updraft continues to feed the storm, but
precipitation begins to fall out of the storm,
creating a downdraft (a column of air pushing
downward).
– The mature stage is the most likely time for
hail, heavy rain, frequent lightning, strong
winds, and tornadoes. The storm sometimes
appears black.
Formation – Stage 3
• Dissipating Stage
– Downdraft begins to overcome the updraft. Rainfall
decreases in intensity, but lightning remains a danger.
– Stages of a thunderstorm
Question…
• What are the 3 main ingredients for
thunderstorm development?
•
•
•
•
A. Moisture, cold air, and lift
B. Moisture, warm air, and lift
C. Dry air, warm air, and lift
D. Dry air, cold air and lift
Question…
• What are the 3 main ingredients for
thunderstorm development?
• A. Moisture, cold air, and lift
• B. Moisture, warm air, and lift
• C. Dry air, warm air, and lift
• D. Dry air, warm air and lift
Frequency of thunderstorms
Types of thunderstorms
• There are 3 types
of thunderstorms
– Single-cell
– Multi-cell
– Super-cell
Super-cell Thunderstorms
• highly organized storm with severe
updrafts
• winds can reach 150-170 mph
• different from other storms due to
presence of rotating updrafts that produce
giant hail, strong downbursts (80 mph or
more), straight line winds, and tornadoes
Dangers of Thunderstorms
Thunderstorms can cause
damage by:
• Flash floods
• Lightning
• Strong winds
• Hail
• Tornados (only from a
super-cell)
Flash Floods
• a rapid rise of water along a stream or lowlying urban area
• occur within 6 hours of a significant rain
event
• usually caused by intense storms that
produce heavy rainfall in a short time
• very strong - can roll boulders, uproot
trees, scour out new channels, and
destroy buildings and bridges
Oregon, November 2007
On April 15, 2007, between 5 and
10 inches of rain fell in NJ
Rain Gauging Station on the Hackensack River
Hackensack River flooding in Rivervale, NJ. This photo was taken
BEFORE the river reached its peak!
Elm Street, Hackensack, New Jersey
Route 18 at Commercial Boulevard in New
Brunswick
Easton Avenue, Somerset
Raritan River near the Rutgers
football stadium
Rutgers Crew boat house along route 18
What it should look like 
Route 18
Piscataway – note the hot tub
floating down the street!
What is lightning?
• a gigantic electrostatic discharge between
the cloud and the ground, between clouds,
or within a cloud
• the same kind of electricity that can shock you
when you touch a doorknob (static electricity)
• results from buildup and discharge of
electrical energy between positively and
negatively charged areas.
Lightning strikes
somewhere on
Earth 100 times
every second!
Each year
lightning strikes
the USA 20 million
times!
Most cloud to ground lightning – central Florida
Almost no lightning – Pacific Northwest
How Does Lightning Work?
1. Wind creates friction in an
ice cloud that creates
“static electricity.” The
bottom of a cloud
becomes negatively
charged. Since opposites
attract, positive charges
collect on the ground and
other surfaces under the
cloud.
How Does Lightning Work?
2. A stepped leader —a
negative electrical
charge made of zigzagging segments, or
steps—comes
partway down from
the cloud. The steps
are invisible. Each
step is about 150 feet
long.
How Does Lightning Work?
3. When the stepped
leader gets within 150
feet of a positive
charge, a streamer (a
surge of positive
electricity) rises to
meet it. The leader
and the streamer
make a channel.
How Does Lightning Work?
4. An electrical current from an object on the
ground surges upward through the
channel. It touches off a bright display
called a return stroke.
In this 5 minute
time exposure
photo, lightning
strikes Tucson, AZ.
Each flash
contains 1 billion
volts of electricity,
enough to light a
100 watt bulb for 3
months.
Lightning
• happens in ½ a second
• flash superheats the air to 50,000 ºF,
– 5 times hotter than the surface of the sun!
• causes a shock wave that results in
thunder
– Thunder - the booming sound produced by
rapidly expanding and vibrating air along the
path of the lightning.
Ball lightning occurs
after a ground flash.
The ball is usually red,
orange, or yellow, and
can be as small as a
grapefruit or as big as
a pumpkin. The ball
hovers or darts briefly,
fizzles out and ends
with a loud
BANG!
Cloud lightning never strikes Earth.
Spider lightning flashes crawl across the sky for
up to 90 miles.
Benjamin Franklin
• In 1752 the famous scientist and statesman conducted
an experiment that proved that lightning is electricity.
• He invented lightning rods to protect buildings from being
struck and catching fire. Prior to his invention, because
the church tower was usually the highest structure, it
was the building most often hit by lightning. The
buildings burned. Parishioners were told NOT to go to
the church to seek shelter during a storm.
• Lightning starts many fires in the western US and
Alaska.
More modern lightning rods
use guide wires to send the
electrical charge safely into
the ground.
Parents “ground” their
children. Get it?
Lightning Safety FUN FACT
The Empire State Building
in New York City is struck
on average more than 100
times per year. The
building is actually
designed to simulate a
giant lightning rod in order
to help protect the other
buildings in the
surrounding area.
Where and when are you most
likely to be struck?
• Florida has twice as many lightning
casualties as any other state.
• Most lightning casualties occur between
noon and 4 p.m.
• Sunday has 24% more deaths than other
days, followed by Wednesday.
• Lightning reports peak in July.
Who is most likely to be struck?
• Men are struck by lightning 4 times more
often than women. Males account for 84%
of lightning fatalities and 82% of injuries.
• Victims suffer from paralysis, memory loss,
burns, loss of sight or hearing, and other
neurological problems.
• Only 10-20 percent of lightning victims are
immediately struck dead.
Where is the storm?
• Sound travels more slowly than light, so we see
the lightning before we hear the thunder.
• Count the seconds between a flash of lightning
and the next clap of thunder.
• Divide by 5 to determine the distance to the
lightning in miles.
• By the time you hear thunder, you are already
within striking distance!
How far away is it?
• You see lightning and begin counting.
• You count to 10.
• How far away is the storm?
– 10 divided by 5
– equals 2 miles
If you can hear
thunder you are
already in danger
of being struck by
lightning.
When thunder
roars, go indoors!
Fulgurite
• Sometimes when lightning strikes sand, the
sand is superheated. It melts and then fuses
together to form a fulgurite. These take the form
of tubes, sometimes more than half inch in
diameter, that look like lightning bolts.
• Rock Fulgurites are formed when lightning
strikes the surface of a rock, melting and fusing
the rock.
• The melting point of Si02 is 2950 oF.
Fulgurite
True Lightning Stories
• The Empire State Building and the Sears Tower
are struck thousands of times each year!
• A watermelon on a kitchen table in Arkansas
blew up during a thunderstorm in 1987. A clap of
thunder caused it to vibrate so fast that it
exploded!
• A field of potatoes was struck by lightning. The
potatoes were cooked by the strike. After being
dug up, they were eaten like baked potatoes!