The Celsius dropped below 20 degrees on Friday for the first time this season.
The minimum temperature on Friday was 19.7 degrees, two notches below normal.
The Met office attributed the dip to the cold and dry north-westerly winds entering the city.
The last time the mercury dipped below 20 degrees in Kolkata was in the middle of March.
The cool phase will continue for the next few days because of favourable conditions in northern India, a Met official said.
Kashmir witnessed fresh snowfall on Thursday night.
“The sky is clear. The dry and cold north-westerly winds are getting an unobstructed access into the city. The minimum temperature is likely to remain in the range of 19-20 degrees over the next few days,” said the Met official.
Kolkatans on terraces or balconies celebrating Diwali felt the hint of chill in the early hours of Friday.
But several parts of the city had a gloomy sky on Friday morning.
The sky was enveloped in a layer of smog, attributed to the bursting of crackers the night before.
Winter is still some distance away, the Met office said. Unlike the monsoon, the weather office in Alipore does not announce the onset of winter. There are, however, some parameters that mark the arrival of the season.
One such parameter is that the minimum temperature has to be 15 degrees or lower for at least four days at a stretch.
The cold phase in Kolkata is expected to be temporarily halted from the middle of next week, said the Met official.
“A system is likely to take shape over southeast Bay of Bengal, near the Tamil Nadu coast. Some moisture incursion into Kolkata is likely because of the system. The cold phase will be halted then,” said the official.