The first half of December 2025 has been the coolest in at least a decade, suggest Met readings at Alipore.

The average daily minimum temperature from December 1 to 17 is 16 degrees Celsius (see chart). For a good part of December, the minimum has been between 15 and 16 degrees.

The next few days are unlikely to see any significant change in the conditions, according to the forecast.

The usual minimum temperature in mid-December in Calcutta is 16.1 degrees, the Met office said.

The drop this season may not be apparent, but the difference is in the persistently pleasant weather.

In Calcutta, winter does not usually mean uninterrupted chill. The season is divided into cold spells caused by the free flow of northwesterly winds and warm spells brought by Western Disturbances.

A Western Disturbance is a storm that originates in the Mediterranean region
and enters India via Pakistan. It brings sudden winter rain as it moves from west to east.

“Successive Western Disturbances have taken shape this year, too. But none of them was very active. Usually, a strong Western Disturbance can move from the northwestern Indian to the Northeast. It then causes rain and, on some occasions, snowfall in Sandakphu, the highest point in Bengal and in Sikkim. But so far this month, there has hardly been any rain in the hills of Bengal or in Sikkim,” said H.R. Biswas, who heads the Regional Meteorological Centre in Alipore.

The Western Disturbances this year have mostly gone towards Tibet and China, sticking to a path along the upper reaches of India.

Even states like Punjab, Uttar Pradesh and Delhi have been much less affected by them so far this year.

One such system was behind the season’s first such blanket of dense fog in northern India that forced the cancellation and diversion of hundreds of flights connecting Delhi and caused fatal accidents on the roads leading to the capital.

“A fresh feeble Western Disturbance is likely to affect the Western Himalayan region from the night of December 17. Light rainfall/snowfall at a few/isolated places over Jammu-Kashmir-Ladakh-Gilgit- Baltistan-Muzaffarabad during December 18-22 and over Himachal Pradesh and Punjab on December 20 and 21, and Uttarakhand on December 21,” said a national Met bulletin.

Easterly waves can also disrupt the chill in south Bengal by bringing moisture-laden winds from the Bay of Bengal, which block the colder, drier northwesterly winds and cause temperatures to rise.

“So far this year, easterly waves have also not affected our region,” said Biswas.

The minimum temperature dropped to 14.5 degrees in Calcutta on December 6,
the coldest day so far this winter.

The cold northwesterly winds are dominating the atmosphere. While the Celsius has dropped to 14 degrees in mid or late December in the past, there have been several days when the minimum rose to 20 degrees.

But December 2025 has been steady that way. Barring a few days, the minimum temperature has consistently remained between 15 and 16 degrees.

Calcuttans are not complaining. The mornings have been sunny and pleasant. After sundown, the chill is unmissable.