A negative cloud-to-ground (-CG) flash captured at 7,207 images per second. A negative stepped leader propagates downward from the cloud and connects with the ground causing a bright return stroke. Filmed near Devils Tower, WY
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http://en.wikipedia.org/wiki/Lightning# ... ing_StrikeA lightning strike is like water running down a steep hill or more correctly like charged particles running down a large potential difference caused by the electric field. These electrons are zigzagging through the air as they meet paths of easier passage through the air--paths with a lower dielectric strength. Each stroke of a lightning strike is usually about 50 m (150 ft) long and lasts about 1 to 2 microseconds with a pause of about 50 microseconds before resuming another stroke in a slightly or significantly different direction. The front of a lightning strike is called a stepped leader and may split into many different paths--not all of them reach the ground giving rise to the phrase: forked lightning. The part of the stroke that reaches the grounds nearly always carries most of the charge as electrons rush to the newly found low resistance path. In a typical cloud-to-ground strike, electrons descends from cloud base to ground. Just before the strike leader reaches the ground, the charge in the step leader induces a huge electric potential in objects connected to the ground (some 10's of million volts), that brings up spikes of positive charge flow from high sharp objects, lightning rods, people, trees, etc. connected to the ground.
Excellent illustration of how electrons essentially search through 'open' space, looking for the path of least resistance. What stops it from being a straight line? Airborn particulate matter?
