Had there been no Himalayas, what would have been the winter climate in north India?
Himalayas run across 2500 km in East-West direction, creating a natural wall between Central Asia and Indian sub-continent. In winter, it blocks the cold polar air blowing southwards from Central Asia from entering India, thus keeping India 3° to 8°C warmer than the regions of similar cold latitudes in Asia. Had there been no Himalayas, extremely cold and dry winds would have entered India.
Westerly Jet streams blow roughly parallel to the Tibetan highlands during winter. The Himalayas bifurcate these streams into two branches, of which Southern branch enters North India and gives much needed winter rainfall over the North-West region. Had there been no Himalayas, this Westerly Jet streams would not have entered Indian plains.
Thus, Himalayas play an important role in keeping India warmer and bringing rainfall in winter.