The national capital witnessed another cold morning on Wednesday, with the minimum temperature settling at 10.6 degrees Celsius, four notches below normal. The India Meteorological Department (IMD) said the temperature met the criteria for a cold wave on Tuesday but not Wednesday.
For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal for two consecutive days. On Tuesday, the minimum temperature had dropped to 10 degrees Celsius, the lowest in the season so far. It was less than that of Dalhousie (10.9 degrees Celsius), Dharamshala (10.6) and Mandi (10.2) in Himachal Pradesh and Mussoorie (10.4) in Uttarakhand.
Kuldeep Srivastava, the head of the regional forecasting center of IMD, said a similar situation is expected to prevail for another four to five days. He said the month of November this year is expected to be the coldest in the last four to five years. Normally, the Safdarjung Observatory, which provides representative data for the city, records a minimum of 14.8 degrees Celsius in the first week of November.
The mercury dips to 11-12 degrees Celsius by the last week of November, according to IMD officials. The senior IMD scientist said the minimum temperature is expected to be recorded in single digits in the next three to four days.
Delhi has been witnessing a trend of low minimum temperatures due to the absence of cloud cover, he said. Clouds trap some of the outgoing infrared radiation and radiate it back downward, warming the ground.
Also, there has been snowfall in the higher reaches of Himachal Pradesh in the last three to four days, so cold winds from that region have started affecting Delhi’s weather, he said.
The national capital's air quality improved marginally on Wednesday due to favourable meteorological conditions but was still in the "poor" category.
The central government's Air Quality Early Warning System for Delhi said "fire counts" reduced in Punjab (around 2,400) on Tuesday, but were "still significantly high and are likely to impact the air quality in Delhi-NCR and northwest India"
The share of stubble burning in Delhi's pollution had dropped to 10 percent on Tuesday due to a change in the wind direction. The city recorded an air quality index (AQI) of 279 at 10 am as wind speed picked up.
The 24-hour average AQI was 302 on Tuesday. It was 293 on Monday and 364 on Sunday. An AQI between 0 and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate",201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".