Recent storm news about lightning induced house fires and children and horses killed by lightning may have you wondering what's causing this unusual weather. Well, there is nothing unusual going on at all. However, after years of drought where our normal summertime thunderstorm pattern was suppressed its understandable this seems like something new and different. But it's just perception. Last summer, while not a drought, was by and large ho-hum. Recent destructive lightning storms are a return to more normal weather.
July and August are peak months for electrical storms in Georgia. The build up of heat and humidity is the fuel for the cumulonimbus thunderhead clouds known as thunderstorms. As we get deeper into summer, storms tend to form later in the day or even late night, move slowly producing flooding and big time "light shows".
Lightning kills more people in the U.S. in a typical year than tornadoes or hurricanes, it just gets less media attention and therefore is an under-rated killer. Georgia ranks in the top 10 for lightning fatalities at number nine. A thunderstorm does NOT have to be "severe" to cause lightning strikes on people or animals or to cause house fires. Any thunderstorm can and will do both. If you hear thunder you are in danger of being struck: unless you are in an enclosed hard-top car with windows up, OR in a closed house and not using plumbing or corded phones or appliances. In other words, you are at risk of being hit by lightning if you are outside and hear thunder! Thunder is the acoustic supersonic shock wave sound that lightning makes.
Lightning in the clouds often precedes cloud to ground lighting by anywhere from 5 to 30 minutes. So if you see lightning flashes or streaks in the sky it is an early warning to go indoors immediately, don't wait for thunder or for the first vertical bolt.
Most people and animals struck by lightning are not hit directly but really take an indirect hit when it strikes a tall object nearby and travels to reach someone standing outside. The odds of being struck either way are 1 in 600,000.
Most people who are struck by lightning are not killed, 70% survive. People struck are safe to touch and give first aid, they do not retain any charge. But often they suffer debilitating life long injury such as burns, blindness, brain damage or physical or mental disability or impairment. Lightning does strike the same place twice, in fact there's no limit. When lightning strikes a tree it often flows underground from the tree following the roots, often visibly tearing up the grass in long gashes. Lightning will also travel from a tall object to ground and then follow buried pipes or wires and fences to find its victims. There is no such thing as "heat lightning". That is just regular lightning observed at night too far away for you to hear the thunder. It is no more caused by heat than the bolt that strikes a tree in your yard.
All thunderstorms have lightning, it's what causes the thunder, so if you hear thunder you're in danger if you are outside. Lightning travels farther than the sound of thunder, which is why people get hit when and where it is not yet raining or even get struck by the "bolt from the blue" when the sun is shining. Given the speed differential between light and sound we derive this formula to estimate how far away a lightning bolt was from you: when you see the bolt, count the seconds until you hear the thunder, then divide by 5. This gives you the miles to that bolt.
At any given moment 2,000 thunderstorms are active around the world producing 100 flashes per second. In the U.S. there's an estimated 25 million lightning flashes per year.
There are a variety of theories on the formation of lightning ( electrostatic induction and polarization mechanism hypothesis) but they basically boil down to this: ice and water droplets collide and fracture in a growing storm cloud, as updrafts and downdrafts and gravity act with the earths electromagnetic field to cause positive and negative charges to separate. The hydro-electrification of the cloud and ground occurs as a result increasing the electrical potential within the earths natural electromagnetic field. It builds until the resistance in the air breaks down and a flash discharge begins. The discharge begins from the cloud and from the earth in nearly invisible to the eye ionization stepped-leader streamers, when these two streams connect-- the flash we see as lightning occurs: http://en.wikipedia.org/wiki/File:Leaderlightnig.gif
All things being equal you get more lightning as the vertical height of a storm increases and/or as the convective available potential energy (CAPE) increases based on the thermodynamics and physics of the atmosphere on a given day. Greater instability equals greater lightning generation. If the storms are slow moving as is typical in mid to late summer, then the lightning can go on for hours before a storm dissipates or moves away.
Electrification of a cloud occurs when ice and water co-exist. This can happen if the freezing level is unusually low or if the cloud tops grow unusually high reaching beyond the ice zone. This process accelerates as updrafts in the storm become stronger which happens as the temperature difference increases between the surface and upper atmosphere. Thus the flash rate is proportional to the 5th power of the updraft velocity. Such that a barely noticeable 10% increase in cloud height would have a 60% increase in total lightning flashes per minute.
Most cloud to ground lightning caries a negative charge. The less common positive lightning strike is more destructive, being more powerful and larger coming from higher up in the storm clouds. The air near a lightning strike is heated to 3 times hotter than the surface of the sun: 36,000 degrees F. The lightning channel can reach 50,000 degrees F. The rapid expansion and contraction of that lightning heated air is the cause of thunder. The typical electric channel of a lightning bold is as thin as a pencil, travels 130,000 MPH, carrying 30,000 to 300,000 Amps or one trillion watts.
Technically a lightning bolt is from the earth up AND from the cloud down equalizing an imbalance between positive and negative electrons between the cloud and earth amounting to millions of volts. A lightning flash is composed of a series of strokes with an average of about 4 each lasting about 30 microseconds, so the human eye sees just one flash or sometimes a flickering.
Since all thunderstorm have lightning any thunderstorm can cause house fires or fatal strikes.
While documented lightning injuries in the United States average about 300 per year, undocumented injuries are likely much higher. Here are the safety tips:
* If you're outside, get inside a building or vehicle. If you can hear thunder, you are already at risk.
* Inside a home, don't use telephones or other electrical equipment unless in an emergency.
* Do NOT stand beneath a tall isolated tree, or an open area. If necessary go to a low place such as a ravine or valley.
* Avoid open water, as well as tractors, bicycles, motorcycles, golf carts and especially golf clubs. Cars, trucks and other enclosed vehicles are generally safe if you avoid contact with metal surfaces.
* In a forest seek shelter in a low area under a thick growth of small trees.
* If you are in an isolated area and you feel your hair stand on end, this indicates that lightning is about to strike. Drop to your knees and roll forward onto the balls of your feet. Place your hands on your knees and tuck your head down. Do NOT lie flat on the ground.
* Watch for Developing Thunderstorms: Thunderstorms are most likely to develop on spring or summer days but can occur year round. As the sun heats the air, pockets of warmer air start to rise and cumulus clouds form. Continued heating can cause these clouds to grow vertically into towering cumulus clouds, often the first sign of a developing thunderstorm.
* When to Seek Safe Shelter: Lightning can strike as far as 10 miles from the area where it is raining. That's about the distance you can hear thunder. If you can hear thunder, you are within striking distance. Seek safe shelter immediately.
* Outdoor Activities: Minimize the risk of being struck. Most lightning deaths and injuries occur in the summer. Where organized outdoor sports activities take place, coaches, camp counselors and other adults must stop activities at the first roar of thunder to ensure everyone has time to get to a large building or enclosed vehicle. Leaders of outdoors events should have a written plan that all staff are aware of and enforce.
* Indoor Activities: Inside buildings, stay off corded phones, computers and other electrical equipment that put you in direct contact with electricity. Stay away from pools (indoor or outdoor), tubs, showers and other plumbing. Buy surge suppressors for key equipment. Install ground fault protectors on circuits near water or outdoors. When inside, wait 30 minutes after the last clap of thunder, before going outside again.
* Helping a Lightning Strike Victim: Lightning victims do not carry an electrical charge, are safe to touch, and need urgent medical attention. Cardiac arrest is the immediate cause of death for those who die. Some deaths can be prevented if the victim receives the proper first aid immediately. Call 9-1-1 immediately and perform CPR if the person is unresponsive or not breathing. Use an Automatic External Defibrillator if one is available.
* Summary: Lightning is dangerous. With common sense, you can greatly increase your safety and the safety of those you are with. At the first clap of thunder, go to a large building or fully enclosed vehicle and wait 30 minutes after the last clap of thunder before you go back outside.
When Thunder Roars, Go Indoors!
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