The minimum temperature dipped below normal on January 4, with a reading of 12.6 degrees Celsius. A combination of factors has been responsible for the long, cold run of the northwesterly wind in Calcutta this month. "One of the usual impediments to the northwesterly wind flow that ferries chill to Calcutta are low-pressure areas in the vicinity of the Bengal coast. The previous longest spells of cold weather with below-normal readings were in 2011 and 2013. The minimum temperature never dipped below 18.7 degrees Celsius that time.

Source: The Telegraph January 16, 2018 21:00 UTC