Kolkata airport suffered its first fog disruption of this winter on Wednesday.
Airport officials said the departure of around 40 flights was delayed as operations were stalled between 5.37am and 7.54am. Three flights headed for the city had to be diverted, officials said.
Visibility had gone down to zero as thick fog covered the runways.
Airport sources said visibility had started dropping since early on Wednesday. By 5.37am, it was zero. Operations resumed when visibility started improving at 7.54am, officials said.
However, the delays continued till later in the day. The day’s first flight landed at 8.06am.
Airport sources said among the flights diverted was one of IndiGo, from Bangalore. It was diverted to Bhubaneswar. A cargo flight of SpiceJet was diverted, too.
“This was the first disruption because of fog this season. Last year, we had three to four days of disruptions,” said airport director C. Pattabhi.
The city airport has Category III B instrument landing system, which allows flights to operate at a minimum visibility of 50 metres. The system has reduced disruptions but operations still have to be suspended when visibility drops below 50 metres because of dense fog.
Wednesday’s fog was linked to Cyclone Jawad, said Met officials.
The low-pressure system that Jawad degenerated into has dissipated but the moisture content in the atmosphere is still on the higher side.
“The relatively high moisture content and low speed of the northwesterly winds together led to the formation of the thick blanket of fog,” a Met department official said.
On Wednesday, the minimum relative humidity — a marker of the moisture content in the atmosphere during the driest part of the day — was 69 per cent.
“Winds from districts mixed with the moist air, the vapour condensed and fog formed,” said a weather scientist.
A similar fog cover is expected over the next couple of days, the official said.
“Partly cloudy sky with fog/mist in the morning,” reads the forecast for Thursday.
The moisture content is tipped to go down gradually. As it goes down, the foggy conditions are also tipped to give way to a clearer sky.
The minimum temperature in Kolkata is tipped to reach sub-15 degree levels by the end of this week or the start of the next.