As we go higher from sea-level, air pressure and air temperature both decrease.
Generally air temperature decreases at 1°C for the ascent of 165 metres or by 0.5°C for ascent of every 1000 metres.
Due to the high altitude, the Himalayan peaks remain snow-covered throughout the year, and higher relief gets more rain.
Moist air cools down when it rises and bring rain. With increasing altitude of the mountains in Assam, Meghalaya the rainfall increase.