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the line into your home. Unplug expen-sive
electrical equipment and turn off
computers before an impending storm.
Use of lightning arresters on power
lines serving computers and other
expensive electrical fixtures is highly
recommended.
All structures should be equipped
with lightning protection, usually light-ning
rods mounted on the highest points
of the roof and attached by cabling to
ground rod conductors buried to a level
where moisture exists in the soil. These
systems drain electrical charges that
can develop on a structure.
Sometimes you cannot avoid being
outdoors during a passing storm. If you
feel your hair stand on end it is a signal
that lightning may be about to strike you.
Drop to your knees and bend forward,
putting your hands on your knees. Do
not lie flat on the ground.
Be alert to storm forecasts and devel-oping
storms, and get to safe locations
during stormy conditions.
On the other hand, lightning has ben-efits.
It is an essential element in main-taining
the earth-atmosphere electrical
balance. Lightning converts gaseous
nitrogen in the atmosphere into nitrogen
compounds that are absorbed by rainfall
and deposited on the ground, creating a
fertilizer for our soils. The lightning-ignit-ed
fires that historically swept across the
Midwest’s rich prairie soils, destroyed
encroaching trees and enhanced the
growth of prairie grasses.
Damaging Lightning
On average, nine to 10 people are
killed by lightning in Illinois each year—
more deaths than caused by any other
form of severe weather, including torna-does
and floods. Annually, an average of
18 lightning-related injuries to humans
occur, and many farm animals are killed.
Studies have shown that only 3 per-cent
of all Illinois thunderstorms produce
damaging lightning, and damages from
lightning occur, on average, 14 days
each year. Damaging events are most
common (80 percent) from June through
August, usually occurring between 1
and 4 p.m., and least prevalent from 10
p.m. to 9 a.m.
The distribution of damaging lightning
events is not even across the state.
Although deep southern Illinois has
more storms than anywhere else, it has
had the fewest incidents of damages.
Southwestern and northeastern Illinois
have experienced the most damages,
partly a result of high population density
and from the added storms generated
by the effect of St. Louis and Chicago
on the atmosphere.
Protection Against
Lightning
Statistics show that most deaths are
to persons caught out-of-doors when a
storm strikes. Persons working or relax-ing
outdoors during the storm season
(March-October) need to be alert to, and
continuously monitor, weather forecasts
calling for thunderstorms.
Do not rely on hearing thunder before
going inside. Thunder audibility has a
maximum distance of 5 miles, and since
storms travel at speeds of 20 to 30 mph,
lightning can occur quickly after the first
thunder is heard. Furthermore, thunder
should not be a primary decision for leav-ing
the outdoors as studies of Illinois
storms show that 22 percent of all light-ning
strikes occur without thunder being
heard within 5 miles of the stroke. In
addition, one of the dangers of remaining
outdoors is that a newly developing storm
can occur overhead, and its initial light-ning
can occur with little or no warning.
Another reason for concern is that
some thunderstorms have excessive
cloud-to-ground lightning. Illinois State
Water Survey studies show that 50 per-cent
of all lightning strokes come with
only 12 percent of the thunderstorms.
These are truly lightning storms.
When a storm approaches, seek
shelter. Farmers should get off tractors
and other metal farm equipment. Chil-dren
should be brought indoors. Do not
stand near or beneath a tree.
The safest place to be during a light-ning
storm is inside a well-grounded
structure but precautions should be
taken there, also. Avoid using the tele-phone
since lightning strikes can hit the
wires and high voltage can move over
Lightning damages in Illinois:
Rural areas experience the most
damage: farm buildings, 82 percent;
rural schools and churches, 9 percent.
Damages in cities with a 100,000
population or more: residences, 40 per-cent;
commercial structures, 23 percent;
industrial buildings/facilities, 22 percent.
Annual financial losses resulting
from lightning in Illinois:
Fires to forests and uninsured prop-erty
= $2-3 million
Repairs to power and communica-tion
systems = $6-7 million
Damage to in-house electrical fix-tures
= $1-2 million
Insurance payments for damages to
property = $38-40 million
Nationally, annual losses from
lightning:
Airline operating costs and delays =
$2 billion
About 300,000 claims handled by
one major insurance company = $330
million
Power outages = $1 billion
Illinois
Thunderstorm
Facts
Thunderstorms occur somewhere in
the state 85 to 90 days each year.
A given place in southern Illinois
averages 60 storm days a year com-pared
with 40 storm days a year at a
given northern Illinois location.
A typical thunderstorm path is 5 to
10 miles wide and 20 to 50 miles long.
Storms typically last 1 to 3 hours.
There are several hundred lightning
strikes in each storm.
The annual average number of light-ning
strokes hitting in a square mile in
Illinois is 10 to 11 in the south, 8 to 9 in
the central and 5 to 7 in the north.
June is
Lightning
Awareness
Month.
Stanley A. Changnon is a senior scien-tists
with the Illinois State Water Sur-vey
based in Champaign-Urbana.
A common type of discharge, sheet or intracloud
lightning occurs between oppositely charged
centers within the same cloud.
Cloud-to-ground lightning helps enrich our soils with
nitrogen compounds necessary for plant growth.
Only 3 percent of Illinois thunderstorms
create damaging lightning, with the most
damaging storms occurring between 1 and
4 p.m. from June through August.
Thunderstorms travel at speeds of 20 to
30 mph. Monitoring weather conditions is
essential when outdoors, such as these
farmers harvesting a wheat field.
(Photo courtesy Illinois State Water Survey.)
(Photo By Paul Hadfield, www.pawleewurx.)
Electronic Documents of Illinois
