lightning

1.What causes lightning?
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 flow of charge (current) produces a luminosity that is very much
brighter than the part that came down. This entire event usually takes
less than half a second.

2.Where does lightning usually strike?
Lightning comes from a parent cumulonimbus cloud. These thunderstorm clouds are formed wherever there is enough
upward motion, instability in the vertical, and moisture to produce a deep cloud that reaches up to levels somewhat
colder than freezing.

These conditions are most often met in summer. In general, the US mainland has a decreasing amount of lightning toward
the northwest. Over the entire year, the highest frequency of cloud-to-ground lightning is in Florida between Tampa and
Orlando. This is due to the presence, on many days during the year, of a large moisture content in the atmosphere at low
levels (below 5,000 feet), as well as high surface temperatures that produce strong sea breezes along the Florida coasts.
The western mountains of the US also produce strong upward motions and contribute to frequent cloud-to-ground
lightning. There are also high frequencies along the Gulf of Mexico coast westward to Texas, the Atlantic coast in the
southeast US, and inland from the Gulf. Regions along the Pacific west coast have the least cloud-to-ground lightning.

Flashes that do not strike the surface are called cloud flashes. They may be inside a cloud, travel from one part of a
cloud to another, or from cloud to air.