Fog grounds Delhi to halt; more in store till weekend: IMD

New Delhi

Very dense fog gripped the Capital from 8.30am to 11.30am on Wednesday, enveloping the entire city in a white blanket of zero visibility that delayed train arrivals, grounded flight take-offs and impacted traffic movement during the morning rush hour, and subsequently had a cascading effect on these operations for the rest of the day.

The India Meteorological Department (IMD) predicted dense foggy conditions to continue till the weekend and issued a yellow alert till January 18. Citing a western disturbance for the development, IMD also predicted light rainfall early Thursday, which will keep the maximum temperature around the 20°C mark.

Although this was not the longest fog spell this winter—this was a nine-hour spell from 11.30pm on January 3 and 8.30am on January 4—it marked the most delayed dispersal and the first time fog extended beyond 9.30am this winter, officials said. IMD classifies visibility as “moderate” when it is between 200 and 500 metres; “dense” when it is between 50 and 200 metres, and “very dense” when it is below 50 metres.

RK Jenamani, a scientist at IMD, said visibility was around 200 metres at the Safdarjung observatory and 150 metres at the Palam observatory around 5.30am, but began to dip after that. “By 8.30am, visibility was between zero at Palam and Safdarjung and below 100 metres at most places in the city. This deterioration in visibility was due to calm wind conditions in the Capital and the surface atmospheric boundary remaining stable. The wind direction was also easterly, so moisture was being fed to the region. Zero visibility lifted only around 11.30am and by 12.30pm too, the visibility was only between 250 and 400 metres,” Jenamani said.

A yellow alert was already in place for the day, but it was upgraded to orange around 8.30am.

The fog spell was preceded by a dip in temperature, with Delhi recording a minimum of 6°C, down from 8.9°C recorded a day earlier and one degree below normal. The maximum was 18.1°C, which was two degrees below normal and down from 21.2°C recorded a day earlier. IMD forecasted Delhi’s maximum to hover around 17°C on Thursday, and the minimum around 10°C.

Travel hit

Over 350 flights were delayed due to zero visibility at the Indira Gandhi International Airport and six were diverted to the Jaipur airport, airport officials said, adding that departures were held as a minimum runway visual range (RVR) of 125 metres was required for operations. Northern Railways said operations of at least 35 trains, to and from Delhi, were delayed by over an hour due to fog.

An airport official said flights can land if the RVR is 50 metres and that on Wednesday, CAT-3 (lowest visibility) procedures were initiated at all four runways. “The RVR at all four runways remained within 75 to 300 metres, keeping a thick cover of fog,” IMD scientist Jenamani said.

At 11.45am, the Delhi airport posted on X, “Due to inclement weather conditions in Delhi, multiple flights have been impacted. We are working closely with stakeholders to assist passengers and minimise any inconvenience caused.”

Around 2.20pm, the airport posted that the visibility was improving and operations were returning to normality.

Officials said the airport initiates low visibility procedures (LVP)—measures aimed at making landing for flights easier when visibility dips below 800 metres—of which CAT-1 is a basic set of precautions initiated for visibility above 550 metres, CAT-2 when visibility is between 275 and 550 metres, and CAT-3, when pilots can land even when visibility is below 50 metres.