Cold and foggy weather persisted in the national capital on Friday as the minimum temperature remained below five degrees Celsius for the third consecutive day, the India Meteorological Department (IMD) said. The Safdarjung Observatory, which provides representative data for the city, recorded a minimum of 4.6 degrees Celsius, three notches below the normal.

"Moderate" fog reduced visibility to 201 metres at Safdarjung. "Shallow" fog was recorded in the Palam area, Kuldeep Srivastava, the head of the IMD's regional forecasting centre, said. According to the weather department, "very dense" fog is when visibility is between 0 and 50 metres. In case of "dense" fog, visibility is between 51 and 200 metres, "moderate" 201 and 500 metres, and "shallow" 501 and 1,000 metres.

Cold wave conditions are predicted in parts of Delhi on Saturday. The temperatures will increase slightly on Sunday and Monday under the influence of a fresh western disturbance affecting the upper reaches of the Himalayas. Moderate fog is likely during this period, Srivastava said.

Cold wave conditions will return December 29 onwards, he 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 the normal.

After Delhi recorded three "severe" air days on the trot, the air quality improved slightly to the "very poor" category on Friday morning. The city's average air quality index (AQI) was 391. The 24-hour average AQI was 423 on Thursday. It was 433 on Wednesday and 418 on Tuesday.

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". A marginal improvement is predicted by Sunday as wind speed picks up under the influence of the western disturbance, Srivastava said.

However, he said, the air quality will dip again, starting Monday due to predicted high humidity, low wind speed and temperatures.