Winter is the season between autumn and spring. By the end of monsoons the temperature falls and it is the coldest season of the year. Meteorological winter is the season that witnesses shortest days and lowest average temperatures.
The year’s coldest months are December and January. In winters temperatures average around 10–15 °C (50–59 °F) in the northwest; temperatures rise as one proceeds towards the equator, peaking around 20–25 °C (68–77 °F) in mainland India's southeast.
A common phenomenon during winters is “Western Disturbances” that causes rains in winters. The main cause behind Western Disturbances is the prevailing of low pressure near Mediterranean Sea.
These winds then move towards India. These winds cause heavy precipitation towards the Southern Himalayas especially in the states of Jammu & Kashmir, Uttarakhand, Himachal Pradesh. Also, the two Himalayan states of Assam and Sikkim also witness heavy snowfall.
During summers the temperature increases due to Sun’s vertical rays directly reaching Tropic of Cancer. Entire India witnesses summers from March to June, while the Northern India experiences it from April to July. April is the hottest month in most of Southern and Central India while it’s May for Northern India.
Norwesters (Pre monsoon Sqaull line thunderstorms) lead to hailstones being dropped during this season. By May, most of the Indian interior experiences mean temperatures over 32 °C (90 °F), while maximum temperatures often exceed 40 °C (104 °F).
While entire India has higher temperatures, the higher altitudes or Hill Stations offer relief from heat due to their as they have comparatively lower temperatures.
Monsoon winds are strong and violent that often changes their direction with season. These winds always flow from colder regions to hotter regions. Monsoons blow from the land toward the sea in winter and from the sea toward land in the summer. The rainfall in India is a result of the South West trade winds that originate from High Pressure areas.
The South west monsoon winds arrive in two branches, namely the Bay of Bengal Branch and Arabian Sea Branch. The Arabian Sea Branch is three times stronger than the bay of Bengal Branch.
The monsoon typically breaks over Indian Territory by around 25 May, when it lashes the Andaman and Nicobar Islands in the Bay of Bengal. It strikes the Indian mainland around 1 June near the Malabar Coast of Kerala. By June, it reaches Mumbai; it appears over Delhi by 29 June.
The Bay of Bengal branch, which initially tracks the Coromandal Coast northeast from Cape Comorin to Orissa, swerves to the northwest towards the Indo-Gangetic Plain. The Arabian Sea branch moves northeast towards the Himalayas.
The months from October to December come under the Post-Monsoon season. During these months there is a different monsoon cycle called the North-east monsoon brings dry and cool air masses to India.
As South west monsoons begin to decrease, climate begins to be drier and the precipitation also decreases. The North East monsoons carry winds that have already lost their moisture while traveling across Central Asia.
However, the states of Tamil Nadu anad Kerala receive good precipitation during the season. parts of West Bengal, Orissa, Andhra Pradesh, Karnataka and North-East India also receive minor precipitation from the northeast monsoon.