Question

after snowfall,the atmospheric temperature decrease rapidly why?

Answer 1

As the sun rays fall on the earth's surface, most of the heat energy is absorbed by the earth's surface.

This in turn hits the air above the earth's surface causing temperature to rise.

However when a snow fall occurs :

Some of the heat energy is reflected back and some of heat is used to melt the snow.

This makes less heat to be absorbed by the air above the earth's source thus leading to a decrease in temperatures.

This explains the concept above.