Despite the reasonably high daytime temperatures, the Indira Gandhi International Airport reported more than three hours of dense fog on Wednesday morning, which disrupted normal flight operations.

Visibility dropped to below 50 metres, while the runway visibility range was reduced to 200 metres on both runways, IGI Airport officials said. As a result, five flights were diverted to other destinations like Jaipur and Lucknow; at least 30 other flights were delayed owing to a backlog to be cleared by the Air Traffic Controller through the day, officials said.

The weatherman at the IGI Airport said the dense fog lasted from 4.50 am to 7.45 am. “The airport received Category IIIB dense fog, when visibility dropped to 50 metres, and runway visibility range was less than 200 meters,” Dr R K Jenamani, director-in-charge of IGI Met department, said.

He said the meteorological conditions made this the season’s first dense fog condition, which resulted from cloudy skies and atmospheric moisture over Delhi in the past few days.

“This is a rare condition and has occurred in Delhi after almost 10 years,” Jenamani said. “The moisture and clear sky on Tuesday night resulted in radiation pulling, which became favourable for formation of dense fog in the morning.”

Jenamani said such conditions normally occur in November. No fog is predicted for Thursday, he said.

An airport official said at least 10 early-departure flights had to be rescheduled and delayed and more than 20 arrivals had to be diverted.

“The fog was most dense at 5.41 am,” Jenamani said. “Runway visibility range had dropped to 200 metres for over three hours on both runways, 28 and 29.”