New Delhi, Dec 29 : Over the past few days, dense fog has engulfed the city, especially in the mornings. A layer of fog blanketed the national capital and its adjoining areas even on Friday morning with moderate to dense fog in isolated pockets of Delhi. Visibility is likely to improve over the day and the minimum temperature recorded stands at 10.7 degrees Celsius -- four notches above the season's average, the India Meteorological Department (IMD) said. 'Dense to very dense fog conditions are very likely to continue during night/morning hours in many parts of Punjab, Haryana, Chandigarh, Delhi and some parts of Uttar Pradesh during Thursday night till Saturday (December 30) morning and in some parts for subsequent three days,' said the IMD. The IMD classifies fog intensity into four types -- shallow, moderate, dense and very dense fog. The visibility ranges from 999m to 500m, 499m to 200m, 199m to 50m and < 50m, respectively. Delhi's Palam station recorded 150m and Safdarjung 200m visibility, according to IMD. As the day unfolds, the fog is forecasted to gradually dissipate, revealing a clearer atmosphere by the afternoon. Flight and train schedules are also being affected, with many flights experiencing delays and some possibly facing cancellations. Over 60 international and domestic flights arrival and departure faced delays, owing to low visibility. In a fog-induced challenge for commuters, several trains arriving in the Delhi region are also dealing with delays, causing frustration among passengers. Delhi's air quality remained in the 'severe' category. The AQI scale categories levels from 0 to 500, with Anand Vihar breaching the 'severe' threshold. At the Anand Vihar area, PM2.5 levels remained into the 'severe' category standing at 473 and PM10 reached 447, and CO plummeted to 107, classified as 'moderate', according to the Central Pollution Control Board (CPCB). The Air Quality Index (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'. The Indira Gandhi International (IGI) Airport T3 witnessed PM2.5 levels at 425 and PM10 at 405, both falling under the 'severe' category. The CO level was recorded at 104, maintaining a 'moderate' rating. /IANS