Morning walkers on the Maidan brave the fog to limber up on Monday. Morning traffic along several stretches was thin and slow because of the heavy fog cover. Picture by Bishwarup Dutta

A blanket of fog enveloped Calcutta from Sunday night, giving the winter-starved city a feel of the season but playing havoc with travel schedules.

More than 25 flights out of the city were delayed by two hours on an average as the airport remained swathed in fog from around 11pm on Sunday till late on Monday morning. A Kingfisher flight from Mumbai landed without trouble around 11.30pm but had to be towed away to the parking bay from the primary runway because the pilots couldn’t see beyond 50 metres.

Only one flight was cancelled — the Jet Airways morning service to Port Blair — but there wasn’t a passenger who wasn’t affected by the fog. Trains to and from Howrah and Sealdah stations were delayed, too.

The Met office said winter hadn’t set in yet but forecast a drop in temperature over the next few days. “Condensation of moisture fed by wind from the Bay of Bengal caused the fog,” said T.K. Chakraborty, the director of the meteorological station at the airport.

“The density of fog will decline in three to four days after the western disturbance blows over. The North Wind will then blow unhindered,” he explained.

The city has been experiencing a warm December, with the minimum temperature reaching record highs. Last Friday, the minimum temperature was 22 degrees Celsius, eight points above normal and the highest for a December day in five decades. The minimum temperature on Monday was 18.4 degrees, four points above normal.

Calcuttans pining for winter may have rejoiced at the sight of a misty morning but the sudden fog invasion triggered panic at the airport.

As visibility dropped rapidly on Sunday night, even the CAT II instrument landing system installed last year couldn’t ensure normal runway operations.

“The CAT-II instrument landing system enables aircraft to land with a minimum visibility of 350 metres. Visibility was less than 50 metres after midnight,” an airport official said.

International flights scheduled to take off early on Monday were hit the hardest. Lufthansa’s Calcutta-Frankfurt and the Thai Airways Calcutta-Bangkok flights were grounded through the night. The Lufthansa aircraft took off at 5.48am and the Thai Airways plane at 6.52am.

Singapore Airlines had anticipated the problem and advanced its Singapore flight from 11.45pm to 10.30pm from December 1. Thai Airways also advanced the departure of its Bangkok flight from 1.55am to 10.30pm.

Flights on the domestic sector were stalled till 8am. IndiGo’s flight to Mumbai took off at 8am, two hours behind schedule. Air India’s flight to Silchar took off at 8.10am instead of 5.40am. The airline’s Delhi flight rolled out of the parking bay at 8.30am, one-and-a-half hours behind schedule, but could not take off until 8.50am because of congestion on the runway.

Devraj Chakravorty, a Delhi-based IT professional, was one of those who suffered because of fog-induced delays. “My Jet Airways flight was to take off from Delhi at 9.20am but was delayed because of the fog in Calcutta. I arrived in Calcutta at 1pm instead of 11.05am, forcing me to reschedule all my appointments,” he said.

Suburban trains from Howrah and Sealdah stations were delayed by half an hour on an average, an Eastern Railway spokesperson said.

Long-distance trains like the Black Diamond Express and the Howrah-Ranchi Shatabdi Express were also affected. Inbound trains from north India and north Bengal were delayed by four hours on an average.

The Rajdhani Express to Howrah and Sealdah, Jodhpur Express, Chambal Express and the Darjeeling Mail arrived several hours behind schedule. The departure of several trains was postponed.