As predicted by the IGI Airports Meteorological department last week,dense fog descended around the airport late Saturday evening.
As many as 100 flights were delayed by over two hours after the runway visibility range (RVR) suddenly dipped.
Normal visibility was also low after 10 pm on Saturday.
At least 23 flights (11 domestic and 12 international) had to be diverted to other domestic destinations,whereas eight were cancelled and five others rescheduled.
Last week,the Met department had predicted dense fog over airport from January 17 to 20 despite cloud cover and rainfall.
The IGIA experienced a fresh spell of dense fog from 9.30 pm on Saturday night to 6 am on Sunday when normal visibility was below 200 metres and RVR was below 800 metres, R K Jenamani,director-in-charge of the IGI Met department,said.
Visibility further dropped to near zero and RVR dipped to below 350 metres at 10 pm on Runway 29 and at 11 pm on Runway 28,Jenamani said.
Category III-B fog descended over the airport after 11 pm till around 4.30 am,during which the RVR fell to between 75-125 metres.
Despite an overcast sky,the airport experienced Category III-B fog,though it was weakened by 4 mm of rainfall from 5.20 am till around 7.51 am, Jenamani said.
Dense fog conditions led to the implementation of low visibility procedures (LVP) at 10 pm on Saturday till about 7.40 am,sources said.
At least 34 flights operated under Category I conditions during LVP. Two flights operated under Category II,four flights used Category III-A,while 18 others operated using Category III-B instrument landing system, an airport official said.
With a huge backlog of flights waiting to be cleared,flights were delayed till late afternoon.
The new Runway 29-11 could yet again not be used for operation during LVP,forcing ATC to conduct all arrivals and departures only on Runway 28-10.
Since most international flights from the Delhi airport operate at night,their operations were the worst affected,sources said.
Eight early-morning flights to Hyderabad,Coimbatore,Mumbai,Kochi,Jaipur,Goa,Bhopal and Indore were cancelled.