Cold Weather Season

This season usually begins with late-November in northern India. January is the coldest month over most parts of the country as sun shines vertically over the Tropic of Capricorn in the southern hemisphere.

During these months, the mean daily temperatures remain below 21°C over northern plains and northern mountain regions. The night temperatures sometimes fall below freezing point resulting in wide spread damage to the standing crops due to frost.

The temperature increases as one moves from north to south. As a result of low temperatures, a feeble high pressure area develops over northern parts of India. This mild high pressure causes the off-shore Northeast monsoon winds. Their direction in Northern Plains is westerly owing to the relief. These land bearing winds being cold and dry don’t give rain over most parts of the country. However, these winds cause rain along the Coromandel coast since they collect moisture on their way over the Bay of Bengal.

The succession of depressions is another feature of this season. These low pressure systems are called "Western disturbances" as they originate in the Mediterranean region. These depressions move with the westerly jet streams. Covering a long distance over Iraq, Iran and Pakistan, they reach India around mid December.

Their arrival results in the increase of temperature and in light rains over northern plains. They cause wide spread snowfall over western Himalayas and the adjoining ranges. At times hailstorms cause widespread damage to the standing rabi crops in northwestern plains. The meager rainfall caused by these disturbances is of great importance to the standing crops, particularly the wheat, in unirrigated areas. These depressions are followed by cold waves which bring down temperatures considerably.

The peninsular India has no well defined winter season. The mean monthly temperatures in the month of January is above 20°C in this part. Moreover, the coastal plains hardly experience any seasonal change as is clear from the mean monthly temperature of above 27°C at Thiruvananthapuram. But Chennai records a temperature of 25°C during December and early January owing to the rains caused by Northeast monsoon winds.

Summary

The important characteristics of cold weather season are:

1. Low temperatures in the north and their gradual increase towards southern parts of India.
2. Blowing of cold and dry northeast monsoon resulting in dry weather conditions in most parts. Coromandel coast receives rainfall during winter.
3. Western disturbances cause light rain in northern plains and snowfall over the Himalayan ranges.