Lightning originates around 15,000 to 25,000 feet above sea level when raindrops are carried upward until some of them convert to ice. For reasons that are not widely agreed upon, a cloud-to-ground lightning flash originates in this mixed water and ice region. The charge then moves downward in 50-yard sections called step leaders. It keeps moving toward the ground in these steps and produces a channel along which charge is deposited. Eventually, it encounters something on the ground that is a good connection. The circuit is complete at that time, and the charge is lowered from cloud to ground.
The return stroke is a flow of charge (current) which produces a luminosity much bright
Thunder is caused by lightning. The bright light of the lightning flash caused by the return stroke mentioned above represents a great deal of energy. This energy heats the air in the channel to above 50,000 degrees F in only a few millionths of a second! The air that is now heated to such a high temperature had no time to expand, so it is now at a very high pressure. The high pressure air then expands outward into the surrounding air compressing it and causing a disturbance that propagates in all directions away from the stroke. The disturbance is a shock wave for the first 10 yards, after which it becomes an ordinary sound wave, or thunder.
Thunder can seem like it goes on and on because each point along the channel produces a shock wave and sound wave.
It's not clear what the maximum possible distance might be. Lightning has been known to strike more than 10 miles from the storm in an area of clear sky above.
Recent research from Vaisala-GAI's LDAR and LDAR II lightning detection networks show that lightning can travel 60 miles or more. They find the longest bolts originate in the front of a squall line and travel 62 miles horizontally back into the trailing stratiform region behind the squall line. The longest bolt they have seen to date was 118 miles long in the Dallas-Ft. Worth, TX area. Since 3-D lightning measurements are relatively new, however, scientists are learning more every day and these numbers may change.
Cloud-to-ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole, or other tall object. It is not known if all people are killed who are directly struck by the flash itself. In addition, flashes may conduct their current through the ground to a person after the flash strikes a nearby tree, antenna, or other tall object. The current also may travel through power or telephone lines, or plumbing pipes to a person who is in contact with an electric appliance, telephone, or plumbing fixture.
Similarly, objects can be directly struck and this impact may result in an explosion, burn, or total destruction. Or, the damage may be indirect when the current passes through or near it. Sometimes, current may enter a building and transfer through wires or plumbing and damage everything in its path. Similarly, in urban areas, it may strike a pole or tree and the current then travels to several nearby houses and other structures and enter them through wiring or plumbing.
The most important statement for everyone to understand, memorize and to act on is: NO PLACE OUTSIDE IS SAFE from lightning NEAR THUNDERSTORMS!
Level-1: Plan your activities around the weather to avoid the lightning strike hazard. If you are going to be outside, know the weather forecast beforehand. Know the local weather patterns.
Level-2: While outside, use the "30-30 Rule" to know when to seek a safer location.
Level-3: Go to a safer location when required. Don't hesitate; go to a safer place immediately! The safest place commonly available is a large fully enclosed substantially constructed building, e.g. a typical house. Once inside, stay away from any electrical conducting path from the outside, e.g., corded telephones, electrical appliances, and plumbing. If you can't get to a substantial building, a vehicle with a solid metal roof and metal sides is a reasonable second choice. Avoid contact with conducting paths going outside. Convertibles and open-framed vehicles do not count as lightning shelters.
Level-4: If you can't get to a safer location, avoid the most dangerous locations and activities. Avoid higher elevations, wide-open areas, tall isolated objects, water-related activities, and open vehicles. Avoid unprotected open structures like picnic pavilions, rain shelters, and bus stops. DO NOT GO UNDER TREES TO KEEP DRY DURING THUNDERSTORMS!
Level-5: USE THIS ONLY AS A DESPERATE LAST RESORT! If you are outside and far away from a safer place, proceed to the safest location. If lightning is imminent, it will often give a few seconds of warning: hair standing up, tingling skin, light metal objects vibrating, seeing corona discharge, and/or hearing a crackling or "kee-kee" sound. If you are in a group, spread out so there are several body lengths between each person. Once spread out, use the lightning crouch - put your feet together, squat down, tuck your head, and cover your ears.
When the immediate threat of lightning has passed, continue heading to the safest place possible. Remember, this is a desperate last resort; you are much safer following the previous guidance and avoiding this high-risk situation.
Level-6: The first step in lightning first aid is to call 999 All deaths from lightning are from cardiac arrest or stopped breathing at the time of the strike. CPR or mouth-to-mouth-resuscitation is the recommended first aid.
No lightning safety guidelines will give 100% guaranteed total safety, but these steps will help you avoid the vast majority of lightning casualties.
Lightning is THE underrated weather hazard. Fortunately, the vast majority of these casualties can be easily avoided.
er than the part that came down. This entire event usually takes less than half a second.