What Causes A Thunderstorm?

Thunderstorms are caused when the weather is very hot and humid. Warm air rises and then cools again very quickly, which in turn produces thunder clouds. Inside these thunderclouds, the violent movement of air causes water droplets and ice to bump against one another, knocking charged electrons from the ice, producing a build up of static electrical charge. The huge amount of energy is finally released in the form of thunder and lighting.
The sound of the thunder we hear on the ground is produced when a strike of lighting produces a huge amount of heat. The lighting has a temperature of around 30,000 degrees centigrade and the air around the lighting expands very quickly. The rapid expansion of air causes the crashing thunder sound. When we get lighting it strikes the ground because the opposite charges of static build up within the cloud and it has to go somewhere. Lighting is looking for something to connect with to discharge its electrical charge. This is why some people get struck by lighting, because basically they are in the wrong place at the wrong time.

From Toastaro,
A thunderstorm is caused when warm air rises and collides with cool air. Example: Hot day. Warm air rises along a cold front. So, a thunderstorm will occur.

It happens with the sight of lightning and its acoustic effect, known as the thunder. Light travels faster than the sound, so you always see lightning first before you hear the rumbling of the thunder. The cloud type that you pictured as dark and downcast is cumulonimbus clouds. Thunderstorms are always accompanied with strong and devastating winds, heavy rains, and sometimes even snow and hails for extreme cases, known by most as snowstorms. Thunderstorms are always caused by the upwards rapid movement of warm dry air. As the warm air moves up, it becomes moist and then it cools and condenses and form dark moody clouds that can reach about 20 km in height. Later, it condenses into water droplets. As the clouds get too heavy, the water droplets fall back down as rain. The falling of the water droplets causes a downdraft of strong and fast wind, and cause the wind-speed near Earth to increase to a maddening speed. Thunderstorm can cause devastating effects, like tornadoes, typhoons, cyclones, flash flood, and hail stones too. Thunderstorm causes strong flashes of lightning and if you are unlucky enough, the strong electric charge of a lightning can electrocute you and kill you if you happen to be strike by one.

A thunderstorm is caused by warm air rising, colliding with cool air.