Shallow fog wrapped parts of the national capital on Tuesday morning, reducing visibility and affecting vehicular movement.
A layer of dense to very dense fog over the Indo-Gangetic plains and adjoining central and eastern parts of the country affected rail and air traffic.
At least 21 trains to Delhi were delayed by one-and-a-half to five hours due to the foggy weather, a Railways spokesperson said.
An official at the international airport here said five flights were diverted to Jaipur on Monday night due to bad weather in Delhi.
The Safdarjung observatory, Delhi's primary weather station, recorded a minimum temperature of 8.5 degrees Celsius, a notch above normal.
The maximum temperature is likely to settle around 17 degrees Celsius.
Moderate to dense fog is predicted in Delhi for the next two days. Coldwave conditions are set to return on the weekend and the mercury may drop to 4 degrees Celsius.
In a statement, the India Meteorological Department (IMD) said dense to very dense fog and cold day conditions were very likely to continue over northwest India during the next four to five days.
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"Coldwave conditions are likely to continue over northwest India during the next three days" and the intensity will decrease thereafter, it said.
According to the IMD, 'very dense' fog is when visibility is between 0 and 50 metres, 51 and 200 metres is 'dense', 201 and 500 metres 'moderate', and 501 and 1,000 metres 'shallow'.
In the plains, the Met office declares a cold wave if the minimum temperature dips to four degrees Celsius or when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches below normal.
A severe cold wave is when the minimum temperature dips to two degrees Celsius or the departure from the normal is more than 6.4 degrees Celsius.
A cold day is when the minimum temperature is less than or equal to 10 degrees Celsius below the normal and the maximum temperature is at least 4.5 degrees Celsius below the normal. A severe cold day is when the maximum is 6.5 degrees Celsius or more below the normal.