According to the Met department, the conditions last week were suitable for the formation of dense fog. The light shower on Monday will decrease temperature but bring back the fog on Tuesday, the weatherman said.

“The light showers were due to the passing western disturbances. The moisture content has now increased and the winds are calm. It will lead to a dip in temperature and increased density and duration of fog,” S C Bhan, director, Safdarjung Met Department, said.

Bhan said the low temperatures last week condensed the air’s water content — formed due to high moisture — and calm winds caused the thick fog. “The temperature has increased by 7 degrees Celsius since the last week. After causing rain and snow in the northern region, the western disturbances have moved towards the eastern parts,” Bhan said.

With a relatively clear weather, Monday was also easier for passengers heading into, or out of, the Capital — at the airport, railway stations and bus stations.

“The Indira Gandhi International Airport had moderate intensity (Category-I) fog from 8 am to 10.30 am on Monday. The rain at 5 am brought down the intensity of fog, which had reduced the visibility to zero on several occasions last week,” R K Jenamani, director-in-charge, IGI Met department, said.

While the fog density on Monday was Category-I, some flights were delayed due to air traffic congestion, as only the main runway was operating till 5 am. Low visibility procedure was implemented for 5 hours due to shallow fog, during which 144 flights (including 117 domestic and 27 international flights) operated.