Delhi's minimum temperature rose to double digits for the first time in 15 days on Friday, but the respite is predicted to end soon.

Twenty trains to Delhi were delayed and three rescheduled due to dense fog in other areas, a spokesperson of the Railways said.

The Safdarjung observatory, Delhi's primary weather station, recorded a minimum temperature of 10.7 degrees Celsius, four notches above the normal.

The capital had logged a minimum temperature of seven degrees Celsius on Thursday, 6.3 degrees Celsius on Wednesday, 5.6 degrees on Tuesday and five degrees on Monday.

The relief from cold in north India can be attributed to a western disturbance, a weather system characterised by warm moist winds from the Middle East.

With the western disturbance retreating, cold wave and cold day conditions are predicted to wallop parts of Delhi on New Year's eve and the winter chill would intensify further in early January, meteorologists said.

The mercury will drop to six degrees Celsius on Saturday and further to four degrees Celsius by Monday (January 2). Dense fog and cold wave conditions are predicted in parts of Delhi from January 1 to 4, according to the India Meteorological Department (IMD) forecast.

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.

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 meteorological 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 the 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.

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