When Liquid water droplets within a cloud freeze into ice,
	electrical charges develop. Ice crystals become positively
	charged, while the remaining liquid droplets take on a
	negative charge. Soon the whole cloud becomes charged:
	positive charges collect in the icy cloud top;negative
	charges accumulate in the lower, warmer parts of the
	cloud. Normally the ground is also negatively charged, but
	the concentration of electrons in the lower cloud repels
	the negative ground charge(like charges repel; opposites
	attract), leaving positvely charged ground directly	
	beneath the cloud. The gathering electrical charges build
	voltages as high as 100 million volts within the cloud and
	between cloud and ground. Air can seperate voltages as
	great as 3,000 volts per foot,or 15 million volts per mile,
	but when voltage exceed these values, lightning results.

	Lightning begins as a relatively weak and faintly visible
	leader stroke makes its way down from a cloud base to
	(1/100 second later) a tree, the ground, or several targets,
	completing an electrical pathway between cloud and
	ground. A massive return stroke shoots up along the
	leader path at one-sixth the speed of light. Return strokes
	from several ground targets may join several hundred feet
	up, forming branched lightning. The concentration of 
	electricity in a path 1"(2.5cm) across heats the air almost
	instantaneously to tens of thousands of degrees(hotter
	and brighter than the surface of the Sun). We See the
	glowing channel as a cloud-to-ground lightning flash,while
	the sudden heating and expansion of the air makes
	thunder. Other varities, such as in-cloud lightning and
	cloud-to-cloud lightning, discharge in a similar manner.
	Many more cloud lightning discharges occur than flashes
	to the ground; most often-especially at night-lightning
	is seen as illumination inside a storm.

	Distant lightning indicates instability sufficient for a
	thunderstorm to develop. Lightning that is close enough
	for thunder to be heard indicates that a storm may be
	imminent. Sound travels at 5 seconds per mile (3 seconds
	per Km). When a lightning flash is seen and its thunder 
	follows 15 seconds later; the lightning is 3 miles(5 Km)
	away.

	Lightning occurs year-round in warm climates, and mainly
	in summer where winters are cold.