This public info statement was on weatherunderground this a.m., some interesting stuff:
.. Lightning awareness week - the science of lightning...
Lightning remains a random... chaotic and dangerous fact of
nature. Lightning has been seen in volcanic eruptions as
well as extremely intense Forest fires in the west... but is
most often seen in thunderstorms.
At any given moment... there are 2000 thunderstorms in progress
across the Earth. Thunderstorms form as a result of three
parameters: moisture... instability and lift (such as fronts...
sea breezes or mountains) forcing the air to rise. Clouds in a
thunderstorm typically rise to elevations between 30000 and
40000 feet (5 to 7 miles) but can rise in upwards of 60000 feet
Temperatures higher in the atmosphere are much colder and ice
forms within the storm cloud varying in size from ice crystals
to hailstones. These particles move within a storm and collide
with other particles causing separation of electrical charges.
The lighter ice crystals become positively charged and rise to
the top of the storm... while the heavier negatively charged ice
particles and hailstones drop to the lower parts of the storm.
This creates an enormous electrical charge differential.
Also... the moving thunderstorm gathers another pool of
positively charged particles along the ground that travel with
the storm. As the differences in charges increase between the
ground and the lower cloud... positively charged particles begin
to rise up taller objects such as trees... powerlines and homes.
Have you ever been in a storm and felt your hair standing up?
Yes... the particles can move up on you!!! that is natures warning
that you are at the wrong place and could become a lightning
The negative charged area of the storm will send down an
invisible charge to the ground called the "stepped leader".
When it approaches the ground... it is attracted by all the
positive charged particles forming a channel. At that point...
you can see the electrical Transfer from the ground to the cloud
within this channel as lightning.
However... not all lightning forms in the negatively charged base
of a thunderstorm. Some lightning originates in the positively
charged upper levels of the storm and is called positive lightning.
This lightning is particulary dangerous because it usually travels
away from the rain core ahead or behind the storm at distances as
far as 10 to 15 miles away from the storm. Thus... lightning can
strike where no rain is falling!!!
Thunder is the result of a lightning strike and is created when
lightning heats up the air around it... up to 50,000 degrees and
causes the air to rapidly expand and contract. The speed of light
is much faster than the speed of sound. To estimate your distance
from a lightning strike... count the number of seconds between
witnessing a lightning Bolt and the sound of thunder... then Divide
by 5. The end result will be the distance in miles you are from
that particular lightning stroke.
Here is a safety tip using what you have just Learned... the "30/30
rule". At the beginning of a storm... when you see lightning...
count the time until you hear thunder. If the time is 30 seconds
or less or you Don not see lightning but hear thunder... seek safe
shelter. Also... at the end of the storm... wait 30 minutes or more
after hearing the last thunder before leaving the shelter.
Additional lightning information can be found on the internet
at NWS Lightning Safety
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Thread: More on Lightning