In Delhi, the average maximum temperature for December was less than 20°C until December 27. This has happened only four times in the last 118 years, and the IMD has said this month would most likely become the second coldest December for Delhi since 1901. A cold-day condition is said to prevail when the maximum temperature during the day is at least 4.5°C below normal. If the maximum temperature is at least 6.5°C below normal, it is classified as a “severe” cold day.
The possible explanations of such extreme conditions are as follows:
Low clouds: This extended cold spell has been triggered by Stratus clouds hanging low over a large geographical area stretching all the way from Pakistan to Bangladesh. The north-south width of the Stratus blanket is 500-800 km, affecting all of North India.
Western Disturbances: Moderate to intense western disturbances, occurring frequently, have contributed to the severe cold over all of North India. Also, the flow of northwesterly winds over Northwest India, at a low height, has increased the chill factor, making days much colder than normal during December.
Climate Change: This cannot be discounted. The unusually cold December this year could just be another instance of extreme climates becoming more frequent, a result of climate change. Across the world, the frequency and intensity of both heatwaves and cold waves have increased over the last several years, and are predicted to increase further