A cold day is declared when maximum temperature is less than or equal to 16°C and foggy conditions prevail which creates cold conditions for prolonged period. Unlike a cold day, a cold wave is created due to wind chill which brings down the actual minimum temperature depending upon the wind speed. If wind chill effective minimum temperature (WCTn), which is basically the effective minimum temperature due to wind flow is 10°C or less, then a cold wave is declared. The minimum temperatures during the last three days have remained around 1-3°C causing severe cold wave conditions across North India. In terms of total number of cold days, December has recorded 14 cold days so far, as against the highest of 17 days in December of 1997, which remains the coldest December, the national capital ever witnessed.

Source: Mint December 31, 2019 09:11 UTC