The National Capital recorded its coldest day of the season on Wednesday with a peak temperature of 15.6°C as icy winds and a band of heavy fog in the higher altitudes kept the city in the thick of winter.

The maximum was 4°C lower than the average, and not 4.5 degrees – the threshold at which it qualifies for a “cold day” -- but an analysis of ambient temperatures taken every three hours since December 31 shows the city is colder than the peak highs suggest, and those figures are outlier recordings of when the sun briefly broke through the fog.

The peak temperature usually comes at a point somewhere in between 3pm and 4pm.

The three-hour readings recorded by the India Meteorological Department (IMD), show the ambient temperature to be in the low double digits (10-11°C) for most parts of the day between 8.30am and 5.30pm, except for some hours between 2.30pm and 5.30pm.

Mahesh Palawat, vice president of Skymet said, "constant shallow fog or haze in the upper layer” has blocked most of the sunlight from reaching the ground. “Except for two hours in the middle of the day, that is between 2pm and 4pm, there is very low amount of sunlight reaching past this upper haze which is why temperature drops so quickly after 4pm."

The maximum recorded at the station was 15.6°C. The station recorded a low of 7.3°C in the early hours.

Multiple weather stations in Delhi recorded cold day conditions. Lodhi Road recorded a maximum of 14.6°C, Ridge recorded a maximum of 13.6°C while CDO Ghaziabad, Noida and SPS Mayur Vihar recorded a maximum of 11.5°C, 12.5°C and 12.3°C respectively. The minimum at all the stations remained below 10°C.

Health experts said prolonged exposure to such cold can be physically stressful for some people. “The blood vessels tend to shrink when it is biting cold, making it difficult for blood to flow smoothly. People may face breathing difficulty and those who already suffer from any heart ailments run a higher risk,” said Dr Upendra Kaul, chairperson, cardiology, Batra Hospital & Medical Research Centre.