The Celsius is set to dip in the city from Wednesday, thanks to snowfall in northern parts of the country.

After staying on the higher side for the past few days, the temperature will go down gradually over the next few days and is tipped to breach the 20-degree mark by Friday, said a Met official.

November began with snowfall in Himachal Pradesh and Uttarakhand. Delhi recorded a minimum temperature of 10 degrees on Tuesday, the lowest this season.

“The cold and dry winds from north India have started entering south Bengal. The minimum temperature in Calcutta will dip gradually. By Friday, it is expected to slide to 18 to 19 degrees,” said Ganesh Kumar Das, director, India Meteorological Department, Calcutta.

Winter, however, is still some distance away, the Met office said. Unlike the monsoon, the Regional Meteorological Centre in Alipore does not announce the onset of winter. There are, however, certain parameters that mark the arrival of the season.

One such parameter is that the minimum temperature has to be 15 degrees or less for at least four days at a stretch.

The monsoon withdrew from the city on October 28 this year, marked by the first arrival of north-westerly winds. The temperature had then slid to 21 degrees and the minimum relative humidity plunged to under 36 per cent.

But a low-pressure system over the north Bay of Bengal last weekend led to fresh moisture incursion into the city. The moisture-laden winds blocked the flow of dry northwestern winds and led to a rise in the minimum temperature. On Monday, the minimum temperature was close to 25 degrees, three notches above normal.

The minimum relative humidity was close to 60 per cent. Both parameters are set to go down from Wednesday.