How does lightening form?
Lightening starts in the clouds during a thunderstorm. It is a sudden joining of electrical current that forms between a cloud in the sky and an object on the ground that sticks up and is isolated. It is easy to see the way the current joins together between the sky and the ground from the picture below.
Clouds are formed when rising water vapor cools as it rises into the atmosphere. The cloud is usually made up of water and ice droplets that attach to particulates and condense in one spot. As the water and ice droplets get together, they bump against one another at a molecular level. This creates electrical charges.
As the cloud fills up with electrical charges, the protons, or positively charged particles move to the top of it, and the electrons, or negatively charged particles move to the bottom of it. When enough negative charges have been formed on the bottom of a cloud, lightening happens. This is because the opposite negative charge from the bottom of the cloud combines with a positively charged object that is on the Earth like a mountain, a person, or a tree standing alone.