Question

How does the temperature decrease with altitude

Answer 1

As you increase in elevation, there is less air above you thus the pressure decreases. As the pressure decreases, air molecules spread out further (i.e. air expands) and the temperature decreases. If the humidity is at 100 percent (because it's snowing), the temperature decreases more slowly with height.

Answer 2

it is the natural phenomena that temperature decrease when prssure decreases