According to the weather department, very dense fog is when visibility is between 0 and 50 metres, 51 and 200 is dense, 201 and 500 moderate, and 501 and 1,000 shallow.
The Safdarjung Observatory, which provides representative data for the city, recorded a minimum of four degrees Celsius, which was four notches below normal.
The Lodhi Road weather station recorded a low of 3.7 degrees Celsius, according to the IMD. The Safdarjung observatory had recorded a minimum of 3.4 degrees Celsius on Sunday, the lowest this season so far.
The minimum temperature had increased slightly on Monday and Tuesday under the influence of a fresh Western Disturbance affecting the upper reaches of the Himalayas.
”The WD has withdrawn. So, the temperatures are going to drop again,” Kuldeep Srivastava, the head of the IMD’s regional forecasting centre said.
The WD led to light to moderate snowfall in the upper reaches of Jammu and Kashmir, Ladakh and Himachal Pradesh. Another Western Disturbance?is likely to affect the upper Himalayan region from December 26.
Cold wave conditions are predicted in parts of Delhi over the next three days. The mercury is expected to drop to three degrees Celsius by Friday.
Moderate to dense fog is also expected during the period, it said. 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.
Delhi’s air quality was recorded in the “severe” category with slow wind speed and low temperature allowing accumulation of pollutants, according to weather department officials.
No major improvement is predicted till December 26, Srivastava said.? The city’s average air quality index (AQI) was 438 at 9 am. The 24-hour average AQI was 418on Tuesday. It?was 332 on Monday, 321 on Sunday and 290 on Saturday.
Air pollution in the neighbouring cities of Faridabad (414), Ghaziabad (486), Greater Noida (485) and Noida (471) also remained the ‘severe’ zone.
An AQI between zero 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”. Srivastava attributed the?dip in the air quality to slow wind speed, low temperature, and high humidity due to the recent Western Disturbance.