Western disturbances that triggered snowfall on Christmas Day in Shimla after a gap of almost 24 years is playing havoc with the winter in Kolkata.The chill, which gave Kolkatans a miss on Christmas Day, is unlikely to return even on New Year day of 2017, met officials have predicted.Even though the night temperature hasn’t dropped as much, gusts of cold and dry winds since early morning is forcing the day temperature in the city to plummet considerably. Result: the day seems to be colder than the nights.“While the night temperature is hovering at 16 degrees Celsius, which is at least two degrees above normal, the day temperature has dropped at least four degrees below what it should have been during this time of the year,” said a senior official of Indian Meteorological Department’s regional office in Kolkata.Met officials said it is the western disturbances that are behind this rather strange phenomenon.A Western Disturbance is a kind of low pressure area that comes in from west Asia. It triggers rain and snow in north India. Such systems usually develop during winter.“A series of Western Disturbances are sweeping north Indian states such as Jammu and Kashmir and Himachal Pradesh over the past few days. These are coming from Pakistan-Afghanistan area,” said the official.These systems have been blocking the passage of cold northerly winds from sweeping Kolkata. To fill in the vacuum, moisture laden easterly winds from the Bay of Bengal and Bangladesh gushed in. This turned the sky over Kolkata partly cloudy.“While, on one hand, the moisture trapped more heat and helped the mercury shoot up, the cloudy night sky didn’t allow the land to radiate the heat at night that had accumulated during the day.”The result was mists in the mornings which lingered late during the day. The night temperature failed to drop because of the mist and the fog. But when they cleared, the temperature dropped and Kolkatans could feel the chill during the day.“From Tuesday we have been getting some gusts of cold winds from the north as they got stronger which helped the day temperature to plummet during the day. The nights as usual remained warmer than what they should have been during this time of the year,” said the official.“But Kolkatans would feel the chill during the day at least. The day temperature would continue to remain at least three to four degrees below the normal over the next few days,” he said.Earlier this year, IMD in its first winter forecast predicted that temperature would remain in the normal and above normal range this winter.