The city is set to shiver again with the Met office predicting more than a six-degree plunge of the mercury through the weekend.

"The minimum temperature, which rose to 19.6 degrees Celsius on Friday, is likely to drop to 13 by Sunday. The cold is likely to stay for at least the first few days of the next week," said an official of the Alipore Met office. Music to the ears of Calcuttans who have started packing their blankets and woollens and bracing for a prolonged spell of heat and humidity.

The sky turned overcast on Friday afternoon and the cold northerly wind that had almost died down a few days ago gained momentum.

There was even a hint of a drizzle in some parts of the the city, while neighbouring districts received smart showers.

"The weather was pleasant on Friday afternoon after the situation started getting summer-like in the middle of the week. I am regretting the fact that I left my shawl at home because it looks like we will have a chilly late evening," said Jhumur Chatterjee, a schoolteacher who lives in Alipore.

What has the caused the chill to return when everyone thought winter has bade adieu to the city?

"A western disturbance spread over the region was blocking the northerly wind, which brings chill to Calcutta, resulting in the recent Celsius surge. But the wind system has passed over Bengal and moved to the north-eastern states. This has cleared the way for the cold wind to pick up speed," said Gokul Chandra Debnath, director, India Meteorological Department, Calcutta.

The western disturbance, coupled with a low-pressure trough, also strengthened the flow of moisture from the Bay of Bengal, leading to the cloud formation and rain.

"The moisture flow has ebbed following the weakening of the western disturbance and disintegration of the low-pressure trough. It's unlikely to rain in Calcutta on Saturday," said a weather official.

With the sky clearing and the relative humidity dipping, the minimum temperature is likely to drop to 17 degrees on Saturday and 13, four notches below normal, on Sunday.

"The seven-degree drop in the minimum temperature in 48 hours will make 13 degrees chillier than usual," said an IMD official.

The last time the mercury dropped to 13 degrees or lower in Calcutta was January 31, when the minimum read 12.6 degrees Celsius.

The normal minimum at that time was 15 degrees Celsius. On Sunday, the normal minimum will be 17.

Friday's overcast condition meant the sunrays were blocked out, resulting in the maximum temperature dropping to 27.7 degrees from Wednesday's high of 31.1.

"Once the fresh spell of chill ends, there is unlikely to be any more this season," said Debnath.