The city spent another shivering afternoon as the mercury was 18.4° Celsius, seven degrees colder than usual, even during the warmest part of the day.

As the sun set, the cold winds became more piercing.

Monday marked the beginning of a fresh round of biting chill, the Met office said.

Many Calcuttans wondered if this was a cold wave. Some were sure it was.

But a Met official clarified it was not.

A cold wave is usually declared in a place when the minimum temperature drops by five degrees or more from normal. It is determined by how cold the night was, not how cold the day felt, said Met officials.

The northwesterly winds started tightening their grip over Bengal from Sunday evening. In the early hours of Monday, the minimum slid to 12.5° Celsius, almost two degrees colder than usual for this time of the year based on a 30-year average.

At 18.4° Celsius, the maximum was 6.7° lower than usual.
It was the second-lowest this winter. December 29 recorded 18.2° Celsius.

Tuesday’s minimum is likely to be colder. The maximum is expected to rise marginally to around 20° Celsius. The usual maximum for early January is 25° Celsius.

One layer of warm clothing proved insufficient for many on Monday. Tea and coffee stalls were crowded. Small fires were lit across the city even before sundown. Few cared that these fires were illegal.

Many schools reopened after the winter break on Monday. Wrapped in woollens, children made a beeline early in the morning.

Several places in Bankura, Birbhum and West Burdwan saw the mercury slide
under 10° Celsius.

Darjeeling had a minimum of 3.4° Celsius.

A Western Disturbance that was over north Sikkim — headed to China — on Monday caused moisture incursion into Bengal. North Bengal is witnessing dense fog.

Apart from some districts like Bankura, Murshidabad and West Burdwan, south Bengal is witnessing shallow to moderate fog.

“The fog is setting in later than expected and persisting longer than it should,” said a Met official.

“The minimum is lower than usual because the fog is settling in late. The maximum is sliding because the fog is staying longer than expected,” he added.

Cold northwesterly winds are dominant near the surface of the earth. That is why the chill is palpable.

Tuesday night is likely to be colder, according to the forecast. The minimum in Alipore could plunge under 12° Celsius, said Met officials.

As the week progresses, the maximum is expected to climb to around 21° Celsius.