Page 34 - 2005 DT 12 Issues

Lightning Most lightning forms in the nega- before you hear thunder. If you see and
tively charged area at the bottom of the hear them together, the storm is over
hunderstorms are harbingers of clouds. Positively charged ice crystals you. Seeing successive strokes in the
change. Another front is rum- move to the top of the cloud, while same place on the horizon means the
Tbling in, bringing new weather the negatively charged crystals fall storm is heading right for you. Once the
along with it. Draw the covers up over to the bottom. As the storm travels, rain reaches you, the number of flashes
your head and hide (make room for it gathers positively charged particles increases, and so does the danger.
the dog, too). But thunder won’t hurt along the ground that travel with it. The deep rumble of distant thunder
you . . . it’s the lightning you need to Tall objects, such as houses, trees, tele- signals the approaching storm. The
worry about. phone poles . . . even YOU . . . collect wind begins to freshen and leaves turn
According to the National Oce- charge which rises up and attracts the their undersides to the sky. Tower-
anic and Atmospheric Administration, ing clouds loom on the horizon. As
lightning is one of the leading weather- the storm draws near, you close the
related causes of death and injury in the windows and bring the kids and pets
United States. The good news is that inside, hoping to hear that “pitter-pat-
there are simple rules you can follow ter” on the roof. You prepare for the
to keep safe, such as staying indoors storm, following all the precautions.
and away from walls, windows and Lightning streaks across the sky, but
doors, plumbing, land-line phones, the rain doesn’t come. Eventually, the
the TV and radio, and electrical appli- storm moves on. It’s just “dry light-
ances. If you’re caught outdoors, find ning” . . . again.
safe shelter in a building or designated Cloud-to-ground dry lightning
lightning-safe field structure. Get in is a major cause of wildland fires in
the car, but avoid touching the metal the West. While not every lightning
sides. As soon as you can hear thunder, strike results in an uncontrolled fire,
there is imminent danger. Lightning can more Western wildfires are started
travel up to 10 miles. When no shelter when atmospheric conditions are dry
is available and the storm is near, lie negative ions in the cloud. A lightning and unstable. Data developed by the
on flat ground or in a shallow ditch, spike rushes to the ground, filling the US Forest Service during the 2000
away from trees and metal structures circuit or “channel” opened by the ris- fire season helped to determine which
or objects (chuck those golf clubs and ing ground charge. Cloud-to-ground storms were more likely to start uncon-
metal-spiked shoes, too). Stay away lightning is the most dangerous. trollable fires in the Pacific Northwest
from water. If you’re swimming, you Not all lightning is negatively and Northern California. Once the link
are a prime target. charged. Some can originate in the to specific atmospheric conditions was
As Ben Franklin learned—and top of the cloud and produce positive established, fire probability maps were
lived to tell about it—when he flew lighting. This is especially dangerous created under the Wildland Fire As-
a kite into a thunderstorm, lightning because it usually strikes away from sessment System to predict fire risk in
is a giant discharge of electricity. The the rain core, well before or after the those regions for a 24-hr. period. The
spark can be as much as 5 miles long storm reaches you (remember that same methods have successfully been
and raise the surrounding air tem- 10-mile strike zone?). If you have an applied in the deserts of the West and
perature to 50,000 degrees Fahrenheit. unobstructed view of the storm, count Southwest. Land managers are able to
That superheated air expands rapidly the seconds between lightning and focus their resources where the likeli-
and . . . “boom!” The most common thunder. A time of 30 seconds means hood of fire is greatest. By factoring in
form of lightning never reaches the the storm is 6 miles away, time to get the amount and condition of available
ground. It jumps from cloud to cloud, inside and stay there for at least 30 fuel, they are also able to calculate
remaining relatively benign, but that minutes. Because light travels much the intensity and speed with which
can change fast. faster than sound, you will see the flash the fire will spread. System maps are
Page 2 FORRC/May 2005