New Delhi, Feb. 3 -- Over 300 flights were delayed after Delhi logged dense fog for over six hours on Monday morning, a day after patchy light rain was seen in the city as a western disturbance kept moisture levels high. Visibility dipped to 100 metres in parts of the city, with overcast skies persisting through the day keeping maximum temperature below normal. The India Meteorological Department (IMD) has a yellow alert in place for Tuesday, forecasting moderate fog at most places in the city in the early hours and dense fog in isolated pockets. "On Monday, both Safdarjung and Palam saw minimum visibility at 100 metres in the early hours of the day. Fog began to clear up only around 9 am," said an IMD official. IMD classifies fog as shallow if visibility is between 1000-500 m; moderate between 500 and 200 m; dense between 199 and 50 m and, very dense below 50 m. Low visibility procedures were also initiated at the Delhi airport, which impacted flights, causing slight delays. The flight tracking website FlightRadar24 showed over 300 flights were delayed, primarily departures, with the average delay time standing at around 25 minutes. On Monday, Delhi's maximum temperature stood at 17.5degC - five degrees below normal for this time of the year. It was 24.6degC a day earlier. The minimum temperature meanwhile stood at 10.4degC on Monday, which was two degrees above normal. It was 12.1degC a day earlier. However, no cold day was declared despite the massive departure from normal for the maximum temperature, the minimum was not below 10degC. Forecasts show the minimum may touch 7-9degC by Friday, before rising by 1-2degC again over the weekend with another western disturbance expected. The maximum is forecast to hover between 18-21degC till Sunday. Delhi's air quality, which was briefly in the "moderate" category, deteriorated back to the "poor" range by the evening. The 24 hour average air quality index (AQI) stood at 210 at 4 pm, still down from a reading over 265 at 4 pm on Sunday....