LUCKNOW, Dec. 18 -- Air traffic was severely affected due to dense fog, causing cancellations, diversions and significant delays on Wednesday. Two flights were cancelled, one had to be diverted while several domestic and international flights operated hours behind schedule, said officials. Flight 6E 6488, arriving in Lucknow from Delhi, was unable to land at Chaudhary Charan Singh International Airport due to poor visibility. After the air traffic control (ATC) denied landing clearance, the aircraft was diverted back to Delhi. IndiGo flight 6E 2108, scheduled to depart from Lucknow to Delhi at 6:05am on Wednesday, was cancelled due to fog, causing inconvenience to passengers. Several domestic flights arriving in Lucknow were also delayed. IndiGo flight 6E 5264 from Mumbai, scheduled to arrive at 12:35am, landed at 1:20am. IndiGo flight 6E 338 from Pune, due at 6am, arrived nearly 50 minutes late. Air India flight AI 2499 from Delhi, scheduled for 7:10 am, reached Lucknow around 9:45am, nearly two hours behind schedule. Similarly, Air India Express flight IX 1026 from Mumbai, due at 8:40am, arrived about an hour late. Departures from Lucknow were also delayed. IndiGo flight 6E 2219 to Delhi, scheduled to depart at 10:55pm on Tuesday night, eventually took off at 1:25am on Wednesday. In addition, several flights from Lucknow to Dammam, Ahmedabad, Delhi, Mumbai, and Riyadh departed with delays ranging from one to three hours due to adverse weather conditions....