(a) Western disturbances: Western Disturbance is the term used in India, Pakistan, Afghanistan and Nepal to describe cyclones which bring sudden winter rain and snow to the north western parts of the Indian subcontinent. This precipitation pattern is driven by the meeting of the warm Westerlies with the cool dry NE monsoons. The moisture in these storms usually originates over the Mediterranean Sea.
(b) Retreating monsoon : After September 23, the sun moves south of the equator due to which India becomes cooler. The low pressure existing over the Indian sub-continent is gradually replaced by high pressure. As a result, the monsoon decreases in intensity. The methodical withdrawal of the south west monsoon from the Indian sub-continent is called retreating monsoon or retreating south-west monsoon.
(c) Orographic Rainfall : When a cloud is encountered by a mountain, it rises on the windward side. The temperature towards the top is less on account of altitude. At a lesser temperature, air loses its moisture carrying capacity and the excess moisture is given off as rainfall. This phenomenon is called orographic or relief rainfall.
