The national capital on December 28 recorded its coldest day of the season as the minimum temperature plummeted to 2.4 degrees Celsius in the morning, officials said.
Dense fog enveloped the city reducing visibility and affecting air traffic and vehicular movement in the streets.
Mercury fell to its lowest in Delhi this season with the Safdarjung Observatory, whose reading is considered the official marking for the city, recording 2.4 degrees Celsius in the morning.
Other observatories recorded as follows: Palam 3.1 degrees Celsius, Lodhi Road 1.7 degrees Celsius, Aya Nagar 1.9 degrees Celsius, a senior MeT Department official said.
Due to very dense fog, zero visibility was reported in Palam Observatory area, which neighbours the city airport.
Due to heavy fog on Saturday morning, four flights have been diverted from Delhi airport, said an airport official.
The official said that the flights are operating at the airport under CAT III B conditions, which means that the runway visual range (RVR) is between 50 metre and 175 metre.
Cold wave and severe cold day has been forecast over Delhi-NCR on Saturday, senior meteorologist at IMD, Kuldeep Srivastava said.
Since 1992, the minimum temperature at Safdarjung Observatory was 2.4 degrees Celsius on December 30, 2013 and 2.3 degrees Celsius on December 11, 1996. The all-time record of low is zero degrees on December 27 in 1930, he said.
With chilling cold continuing to sweep Delhi-NCR, the region is expected to record its second-coldest December since 1901, the weather department had said on Thursday.
"The mean maximum temperature for December was less than 20 degrees Celsius only in 1919, 1929, 1961 and 1997," an official of the India Meteorological Department said.
In December this year, the mean maximum temperature (MMT) till Thursday was 19.85 degrees Celsius. It is expected to dip to 19.15 degrees Celsius by December 31, he said.
Since December 14, most parts of the city have witnessed 13 consecutive "cold days" or a 13-day "cold spell". The last time such a long cold spell was witnessed was in December 1997.
After 1992, Delhi has had cold spells only in four years - 1997, 1998, 2003 and 2014.
"Severe cold day/cold day" conditions are predicted till December 29.