During winter the conditions are reversed. In the cold season the entire land mass of Asia becomes the centre of a very high pressure. An extensive but powerful anticyclone is centered over Mongolia from which cold, dry and stable air out blows in the form of cold waves.
But these cold waves do not reach India because of the protective wall raised by the Himalayas. However, a secondary high pressure system develops over Kashmir and the Punjab. This high pressure area controls the prevailing wind direction over the rest of the subcontinent.
Contrary to the pressure condition over land, there are low pressure centers formed over the Indian Ocean, the Arabian Sea, and the northern part of Australia. In the cold season, therefore, there is pressure gradient from land to sea as a result of which winds begin to move from land to sea. These are the northeast or winter monsoons of northern hemisphere.
In the vast Gangetic Plain the direction of cold winds is north- westerly. In Peninsular India the wind direction varies from north-easterly to easterly. Winds in Sind and Gujarat are usually northeasterly. During winter all over the country the winds are light and variable.
The anticyclonic winds are dry and have no capacity to yield precipitation. Since these winds originate on land and are off-shore, they produce dry and fine weather.
However, certain areas get winter precipitation. The plains of the Punjab and Uttar Pradesh are visited by a number of westerly disturbances which give moderate to scanty rainfall. The area of winter precipitation to the north of parallel 20° N in the Ganges Plain extends up to Patna.
At a matter of rule, the westerly disturbances disintegrate before they reach Bengal. The higher slopes of Himalayan ranges receive heavier rainfall. Higher up in the northern mountainous regions there may be occasional snowfalls.
The southern part of Indian Peninsula receives rainfall from northeastern monsoon currents. These currents while travelling over the Bay of Bengal pick up moisture from the warm ocean surface. The amount of winter rainfall on the eastern side of the peninsula is much heavier than that on the other side.
It may be mentioned here that the shallow depressions giving winter precipitation to the northern plain of India are of different origin. Some of these cyclonic storms are of Mediterranean origin, and they travel to the Indian sub-continent via Palestine and Afghanistan.
On the other hand, a number of storms may originate in the highlands situated to the west of the sub-continent. The Central Asian high pressure system forces them to follow a more southerly track. Later on, their movement is controlled by the Himalayas.
During winter all the pressure-and wind-belts are displaced to the south with the result that the equatorial belt of calm also shifts to the south of equator. Therefore the winter monsoon rain forces the northeastern trade wind in certain parts.