Central Florida is often referred to as the 'Lightening Capital of the US.' It's well documented, too. A typical Central Florida Summer usually brings frequent afternoon Thunderstorms, and they are just chocked-full of lightening. It's not uncommon for the weather service to record lightening strikes in the thousands per hour during these storms. Last week, we had one that produced 5,100 strikes during a single hour.
As June 21 - 27 is Lightening Safety Awareness Week, ther Servie in Melbourne is issuing a primer on lightening this week, with daily installments, which I'll try to remember to post here for our cruisers who visit our area as they prepare to sail out of Port Canaveral.
In any given year, lightning kills more people than hurricanes and
tornadoes combined. Nationwide, it is the second most deadly
weather phenomenon. In Florida, it is the first. Even so, the
threat posed by lightning is underappreciated by most people. One
major reason is that lightning usually does not kill in large
numbers, but rather one or two at a time.
Lightning strikes the ground an estimated 25 million times each year
in the United States. The average Bolt carries about 20 thousand
amps of electric charge... 100 million volts of potential... and can
reach a temperature on the order of 50 thousand degrees fahrenheit.
Tuesday's discussion will center around how lightning forms and
where it strikes.
Lightning is the leading weather hazard in Florida. Over the past
ten years, lightning has killed 7 people in the east Central
Peninsula and injured another 72. However, despite being part of
the nation's most active lightning region, most of these casualties
could have been avoided using basic safety measures. Wednesday's
and thursday's discussion will focus on lightning safety... what to
do and equally important... what not to do... should lightning
threaten your area.
Lightning is a serious threat to people in east central Florida...
especially during the Summer months. Using basic common sense...
most lightning deaths and injuries can be avoided.
The average lightning Bolt carries around 20 thousand amps of
electric charge, 100 million volts of electric potential, and can
generate a temperature in excess of 50 thousand degrees
fahrenheit... hot enough to melt sand into glass. The average peak
power output of a lightning Bolt is about one terrawatt (or 1,000
gigawatts). Furthermore... all of this energy is concentrated in a
channel that usually is no larger than a U.S. Quarter. This energy
density is unmatched in the human world... exceeding even the most
powerful nuclear reactors.
Lightning occurs in the earth's atmosphere 40-50 times a second,
for a total of 1.4 billion strikes per year. Lightning detection
systems across the nation record an average of 25 million
cloud-to-ground strikes in the United States each year.
Lightning has been observed in volcanic eruptions, intense Forest
fires, heavy snow storms, and large hurricanes. However, it most
often occurs in thunderstorms. A thunderstorm needs three components
in order to form: moisture, instability, and a source of lift (such
as a cold front or a sea breeze boundary). Sustained rising
motion within a storm can allow the cloud to build to a height
50 to 60 thousand feet... or 6 to 10 miles above sea level.
Temperatures in the middle and upper atmosphere are much colder than
at the surface, with freezing levels usually no higher than 18
thousand feet. These cold temperatures allow ice crystals to form
in the higher portions of the cloud. Ice is a key element in the
development of lightning.
Within a thunderstorm, the ice particles vary in size from small
crystals to large hailstones. Rising air carries liquid water above
the freezing level, while sinking air pushes frozen particles below
the freezing level. When these collide, electrons are sheared off
of the rising particles and collect on the sinking particles (a
similar effect occurs by rubbing your feet on a carpet). This is
known as "charge separation" and Marks the first step in the
lightning process.
As the positively charged particles rise and the negatively charged
particles sink, an electric field develops within the cloud. At the
same time, the negatively charged bottom of the cloud attracts a
pool of positively charged particles along the ground that shadows
the thunderstorm wherever it GOES.
As the charge separation continues, enormous electric fields develop
between the cloud and the ground, as well as within the cloud
itself. When the field becomes strong enough, a virtually invisible
electric channel, called a "step-leader", will emerge from the
bottom of the cloud. In what can loosely be described as an
"avalanche of electrons", The Channel moves toward the ground,
splitting and forking in a series of steps about 50 meters in length
and one microsecond in duration.
When the step-Leader gets to within 300 feet of the surface, the
pool of positive charge within the ground "reaches" up with a
channel of its own, called a "streamer". When these two connect,
the electric circuit is complete and an intense energy pulse, known
as a "return stroke" races up the connected channel. What humans
see as lightning is actually traveling from the ground into the
cloud! This process may repeat itself several times within a single
channel, giving lightning its flickering appearance. This is called
a "negative stroke", as it lowers negative charge from the cloud to
the ground.
As the return stroke races upward, it heats the air surrounding its
channel to 50000 degrees fahrenheit. This intense and instantaneous
heating causes the air molecules to expand at a rate that exceeds
the speed of sound, known as "explosive expansion". The acoustic
shockwave that results is known as thunder. Lightning will always
precede the thunder, but the time separation between the two will be
shorter the closer you are to the strike. For every five second
delay, the lightning struck about a mile away.
Not all lightning forms in the negatively charged area low in the
thunderstorm cloud. Some of the lightning originates in the cirrus
anvil at the top of the thunderstorm where a large pool of positive
charge exists. Lightning from this area is called "positive
lightning" as it lowers positive charge from the cloud to the
ground. Positive lightning is particularly dangerous for two
reasons: it frequently strikes far from the central rain shaft...
more than 10 miles rare cases... where people may not consider
lightning as a threat. The other problem is it typically has a
longer duration and a much higher peak current than "negative
lightning", making it a much greater risk to life and property.
Outdoors is the most dangerous place to be during a thunderstorm. Most people are struck while working outside, at sporting events, on the beach, or during other outdoor activities. Ten percent of all lightning strike victims die... an average of 60 annually. Of the remaining 90% who survive, most suffer serious long term and often permanent disabilities.
Lightning can strike more than 10 miles from a thunderstorm's central rain shaft. By contrast, the audible range for most thunder is 10 miles. Therefore, if thunder can be heard, lightning is within range. The lightning threat can be greatly minimized by using some basic safety rules:
First... plan ahead. Try to schedule outdoor activities to avoid the
hours of peak thunderstorm activity (usually early afternoon through
early evening). If thunderstorms are forecast, consider canceling or
postponing outdoor activities to avoid being caught in a dangerous
situation.
Second... keep an eye on the sky. Monitor the weather conditions
regularly. Watch for any signs of a developing or approaching
storm... especially if considerable time will be needed to get to a
safe location.
Third... if the sky looks threatening, if lightning is seen, or if
thunder is heard, seek shelter immediately inside a substantial
building. If a substantial building cannot be reached within a few
minutes, then a hard-topped metal vehicle is a reasonable
alternative. Avoid sheds, picnic shelters, baseball dugouts, and
bleachers. Remain in the shelter for at least thirty minutes after
the final thunder is hear before resuming outdoor activities.
The once touted "lightning crouch" is now actively discouraged as
recent studies have found it to have little effect. It is much
better to actively seek shelter than to remain outdoors.
The only time the lightning Crouch should be used would be if you
were lucky enough to get a few seconds warning prior to a strike:
if your hair stands on end, your skin tingles, or you hear a
crackling or static sound, a strike may be imminent. Make yourself
the smallest target possible and minimize your contact with the
ground. Crouch down on the balls of your feet Duck your head, and
cover your ears. Do not lie flat on the ground! Once the lightning
strikes, proceed or continue to the nearest shelter. It should be
noted that the lightning Crouch will not guarantee your safety. It
is a desperate, last ditch attempt to avoid being struck.
Boaters are particularly vulnerable to lightning. Water is an
excellent conductor of electricity and boaters often require several
minutes to reach safe Harbor. In addition, they are the tallest
objects around, be it on a lake, waterway, or open ocean. The
majority of lightning casualties on the water involve open, single
deck boats. Such boat owners need to be acutely aware of the weather
situation. If storm clouds threaten or if thunder is heard, get out
of the water immediately! Do not wait for the rain to begin!
If the boat has an enclosed deck and an approaching storm cannot be
outrun, go below deck and stay away from metal hardware. Disconnect
and do not use radio equipment or any major electronics unless it is
an absolute emergency. If possible, lower, remove, or tie down the
radio antenna and other protruding devices.
It is critical to realize that lightning is the first thunderstorm
hazard to arrive, and the last to leave. Remember... when thunder
roars, go indoors. Remain indoors for at least 30 minutes after the
last clap of thunder (not after the rain ends!). don't be fooled by
clearing skies or emerging sunshine. About 10 percent of lightning
occurs with visible Blue Sky overhead.
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Lightening Capital of the US - Central Florida
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