The Celsius plunged to 14.5 degrees in Calcutta on Friday, going under 15 degrees for the first time in 10 days and living up to the January reputation.

The minimum temperature on January 5 was 13.4 degrees. Ten days of 15-degree plus minimum temperatures in January is extremely unusual in Calcutta, said Met officials.

The warm spell was triggered by a strong Western Disturbance over north and northwest India, that had stalled the flow of north-westerly winds across northern parts of India. The system has since dissipated, leading to a fresh flow of north-westerly winds from Jammu and Kashmir, which has been witnessing heavy snowfall.

After the long warm spell, cold winds have started making their effect felt in Calcutta again from Wednesday. The woollens are back to being visible on roads over the past couple of days.

The Met forecast is mixed — the temperature is tipped to slide marginally over the next 48 hours, then climb up again before another plunge.

“The temperature is expected to be around 14 degrees on Saturday as well. Sunday morning will also be cold. But from Sunday evening, the temperature is expected to rise again,” said a Met official.

A trough of low pressure, tipped to reach Bay of Bengal over the next couple of days, will trigger the flow of easterly and south-easterly winds from the sea towards the direction of Andhra Pradesh, Chhattisgarh, Madhya Pradesh and parts of Uttar Pradesh from Sunday. The moisture-laden winds will again stall the flow of north-westerly winds from Kashmir, the official said.

“The winds (from the Bay) will not directly head towards south Bengal. But they will stall the north-westerly winds that bring chill to Calcutta,” he added.

The only hope in the forecast — the warm spell is expected to be brief.

“The trough is expected to dissipate soon. The warm spell should not last beyond a couple of days. From January 20-21, cold winds will enter Calcutta again and the Celsius will go south,” the Met official said.