It was partly cloudy in the capital on Wednesday with the minimum temperature recorded at 13.2 degrees Celsius, the season's average, the Met office said.
At least seven trains were cancelled, and 26 were running late due to shallow fog in northern India, a railway official said.
"The sky will remain partly cloudy during the day with mist in the morning," an India Meteorological Department official said.
There is no rain forecast for a week, he added.
The humidity at 8.30 a.m. was 91 per cent and visibility stood at 1,000 metres.
The cancelled trains were the New Delhi-Alipurdwar Mahananda Express, New Delhi-Jalandhar Express, New Delhi-Howrah Poorva Express, Delhi-Jammu Tawi Puja Express, New Delhi-Rohtak Intercity, Rohtak-New Delhi Intercity and Delhi-Ferozpur Express.
According to the Delhi International Airport Limited (DIAL), no flights were delayed or cancelled.
Tuesday's maximum temperature settled at 27.7 degrees Celsius, a notch below the season's average, while the minimum temperature was 14.6 degrees Celsius, a notch above the season's average.