What are Western disturbances? How do they affect the climate of India?

What are Western disturbances? How do they affect the climate of India?

The Western disturbances are weather phenomena brought in by westerly flow from the Mediterranean region. They occur in the month of winter and cause rainfall in North and North-Western part of India.
They affect the climate of India in the fallowing ways
(i) By causing cyclonic rainfall in the month of winter, which is otherwise dry, Western disturbance influences the weather of the North and North-Western India.
(ii) Although the amount of rainfall is meagre, it is highly
beneficial to the Rabi crops, especially the wheat.
(iii) They cause snowfall in the mountains.