People in the national capital woke up to a cold foggy Christmas morning with visibility dropping to 50 metres affecting flight schedule and causing cancellation of over 300 trains.The India Meteorological Department has predicted shallow fog for the day with the maximum temperature likely to hover around 21 degrees Celsius. At 8.30 am, the humidity was 100 per cent; visibility dropped to 50 metres at Palam with a spate of flight delays at the Delhi airport. As many as 45 flight departures at the Indira Gandhi International Airport (IGI) was delayed for over an hour due to dense fog.