“The fog this year, coupled with strong winds, is of a variable nature. This fog characteristic is being witnessed in Delhi for the first time —visibility gets completely cleared almost instantly, followed by a fresh spell of dense fog,” an official said.

IGI Met Department said there were fluctuations in the runway visual range (RVR), which made it difficult to function. “General visibility fluctuated between 0 to 200 m from 11.30 pm on Thursday night till about 6 am on Friday morning. The fog finally lifted with strong winds around 6.30 am,” R K Jenamani, director-in-charge, IGI Met Department, said. According to Jenamani, Category-III fog is being experienced, but not in the usual way, since Thursday.

“The fog travelled from runway 29 to 28. On runway 29 (which usually experiences longer and denser spells of fog), Category-III conditions lasted for one hour, from 1.30 am to 2.30 am. On runway 28, the same lasted for two hours from 2.30 am to 4.30 am. Overall, however, the duration and intensity was much less.” The Met department does not expect any significant change in fog patterns in the next 24 hours.