The city spent an unusual January day as a sunless sky and on-and-off drizzles dragged the day temperature down so much that there was hardly any difference between the maximum and minimum temperatures.
Thursday was dark, damp and dreary for most parts. Attendance dipped in schools. Small bonfires were lit in many streetcorners to ward off the chill even in the afternoon.
Metro decodes the weather
Why did it feel so cold on Thursday?
At 16.3 degrees Celsius, the minimum temperature was two notches above normal. But the maximum temperature plunged to 19.2 degrees, a whopping seven notches below normal. The maximum temperature dipping below 20 degrees in January is not common (see chart), said Met officials.
The low day temperature was the main reason for the chill. The minimum temperature is recorded in the early hours of the day, usually just before sunrise, when the city is sleeping. The effect lingers on for a while. But the effect of the maximum temperature — which is recorded in the afternoon, usually when the sun is directly overhead — is felt for most of the day.
The average maximum temperature for January in Kolkata — calculated on the basis of Met readings compiled over the past three decades — is 25.5 degrees Celsius. The average minimum is 14.3 degrees.
“The difference between the two is usually 11 degrees. On Thursday, it reduced to three degrees. For a better part of the day, the temperature was around 17-18 degrees. That is why the chill was persistent and uniform and warm clothes were needed even in the afternoon,” said Ganesh Kumar Das, the director of the India Meteorological Department in Alipore.
January 13 was the coldest day of the season as the minimum slid to 12.6 degrees. But January 13 did not feel as consistently cold as Thursday because the maximum temperature on that day was 22 degrees. It was still a couple of notches below normal but the gap between the minimum and maximum was more than nine degrees.
What caused the low day temperature?
“A western disturbance has led to the formation of a cyclonic circulation over east Uttar Pradesh and adjoining areas. There is a high-pressure zone over the Bay of Bengal. Easterly winds are travelling from the Bay towards the circulation, leading to the formation of rain-bearing clouds over Jharkhand,” said Das.
The clouds are moving towards the Bay of Bengal. They are passing over several districts of south Bengal, including Kolkata. The clouds cloaked the sun throughout Thursday and dragged the Celsius down.
The increased moisture in the atmosphere has, however, stalled the flow of northwesterly winds from Kashmir, the usual agents of chill. But their absence was hardly felt on Thursday.
What is the immediate forecast?
The chill is unlikely to go anytime soon, even without the northwesterly winds.
The current cold spell is the second for Kolkata this winter. The first saw the Celsius sliding in the second week of December. The conditions remained cold for about a week before the northwesterly winds were stalled by moisture-laden winds from the Bay. The conditions started changing from around December 11-12, when the northwesterly winds started coming in again.
“The sky is likely to remain partially cloudy on Friday. The maximum temperature will go up and the minimum will go down, both marginally. Saturday is expected to see a clearer sky. But Sunday and Monday are again likely to be overcast because of the dominance of easterly winds. Some rain is expected in the districts. Rain is not ruled out in Kolkata, either,” said Das.
“The overcast conditions will again drag the day temperature down. When the western disturbance weakens, northwesterly winds are again likely to make a comeback,” he said.