Question

What causes the ice crystals fall from sky during thunder storm in summers?

Answer 1

When ice crystals fall from the sky, it is called a hail storm. These only happen during the summers. 

The reason behind this is that in summers the sun heats up the ground and water vaporizes quickly and forms huge condensed clouds. These clouds grow up into high altitudes, the upper portion of the cloud becomes cold, while the inner portion is hot.  The colder portion forms ice crystals. 

Slowly when there is rainfall, the  ice crystals move downward and get in contact with the droplets. Hence, ice crystals fall during the thunderstorm in summers. 

This is a very natural and usual phenomenon. And happens in summers often.