During winter, the sun is overhead in the Tropic of Capricorn. The land mass becomes cold in North India where the day mean temperature remains below 21 degree Celsius and the night temperature is about 22 degree Celsius. No obvious difference is found in the temperature during day and night.
In the meantime high pressure develops in the northwestern part of India because of prevalence of low-temperature. In contrast to this, a low pressure area forms in the South India, that is both in the Arabian Sea and the Bay of Bengal. Consequently the winds blow from the high pressure area towards South India. These winds are called the ‘Retreating monsoon winds’ which blow from land to sea and do not cause much rainfall. But these winds absorb some moisture while crossing the Bay of Bengal and gives winter rainfall to Tamil Nadu and South Andhra Pradesh.
During this period, a low pressure depression originates over the Mediterranean Sea and travel eastwards across Iran and Pakistan and reach India. This low pressure depressions are called ‘Western disturbances’. The Jet stream plays a dominant role in bringing these disturbances to India. These disturbances cause rainfall in Punjab, Haryana and Himachal Pradesh and snowfall in the hills of Jammu and Kashmir. This rainfall is very useful for the cultivation of wheat.