Why is there lightning and thunder in the sky?

Because there will be friction between clouds in the sky, charges will move and lightning will appear.

Specifically, when the thunderstorm cloud moves to a certain place, the middle and lower part of the cloud is a strong negative charge center, and the underlying surface opposite the cloud bottom becomes a positive charge center, forming a strong electric field between the cloud bottom and the ground. With more and more charges and stronger electric field, a section of air column with strong atmospheric ionization first appears at the bottom of the cloud, which is called cascade leader.

In this short time, a huge amount of electric energy will be released in the narrow lightning channel, which will form a strong explosion, produce shock waves, and then form sound waves to spread around. This is lightning or "thunder".

Thunder must meet three conditions: the air layer has a certain lift and a certain amount of water vapor, and the air layer is unstable, and all three are indispensable. When there is precipitation, there should be enough water vapor in the air layer. Under a certain lifting force, small water droplets will collide into larger water droplets. After repeated cycles, when their weight is greater than the lift of air, they will start to fall, and larger water droplets can fall to the ground.

Because of their respective conditions, it will thunder first and then rain, or it will rain first and then thunder. It doesn't have to thunder before it rains. But in summer, it may thunder first and then rain more. Because its lift is very strong in summer thunderstorms. It takes a long time for water droplets to form to a certain size, and it is greater than the lift force of air.

Extended data

Lightning and thunder are common weather phenomena in summer, while it usually snows in winter. These are two completely different weather phenomena. However, as long as the weather in a certain place has the conditions of snow and thunder at the same time, these two completely different weather phenomena can appear at the same time.

In winter, the sky is overcast, the temperature of the upper clouds is below zero, and the water vapor in the clouds condenses into snow. When snowflakes fall from the clouds, they will melt into raindrops if the air temperature near the ground is high. On the contrary, if the temperature near the ground is low and the snow cannot melt, it will snow.

Thunderstorms are caused by strong convection of warm and humid air in some places. The sharp rise of warm air produces the violent vibration of cumulonimbus clouds, which will accumulate a lot of charges and produce lightning.

Baidu Encyclopedia-Lightning (Natural Phenomenon)