Thunderstorms form when warm, moist air rises into cold air.
The warm air becomes cooler, which causes moisture, called water vapor, to form small water droplets — a process called condensation. The cooled air drops lower in the atmosphere, warms, and rises again.
But the primary reason why it forms
Thunderstorms form when an air mass becomes unstable (when air in the lowest layers is very warm and humid, or air in the upper layers is unusually cold, or if both occur). Rising near-surface air in an unstable air mass expands and cools, making it warmer than its environment, which causes it to rise even farther
Once That happens heavy hail starts to form at the top and light rain forms at the bottom once formed. the light switches places and when they meet in the middle the light gives the heavy negative energy and the heavy gives the light positive energy once finished they start to make lighting inside the clouds. If positive energy is at the ground, lighting will strike on the ground.
Here are some ways you can protect yourself from a really bad thunderstorm. Immediately get off elevated areas such as hills, mountain ridges, or peaks. Never lie flat on the ground. Never make a tree your shelter run inside any building. Never use an overhang cliff as shelter lighting may strike on the overhang falling onto your head. Immediately getting out of and away from ponds, lakes, and other bodies of water lighting may boil the water over 50,000 degrees Fahrenheit.