(Representative image)

KOLKATA: Most of Kolkata spent the weekend discussing the sudden December rain, but few realized that the city experienced something much, much rarer on Sunday: the maximum and minimum temperatures of the day were practically the same.

The minimum temperature recorded by the thermometer placed inside the Stevenson Screen — a wooden box kept outdoors, in order to protect the device from direct exposure to sunlight — was 21.2°C on Sunday, five notches above normal. No one would blame you if you thought the day’s maximum was not that much more. Even the weather office’s equipment found it difficult to trace the mercury’s upward journey; the maximum, at the end of the day, stood at 21.7 degrees, a mere 0.5 degree more than the minimum, and six notches below the normal mark.

Weather officials found it difficult to say when the city had last experienced this type of a day. “It is highly unusual,” said a senior weather bureau official, admitting that the office did not have a ready record of when this had happened last. “A combination of overcast sky, light drizzle and a humidity content of nearly 100% round the clock can lead to this unusual phenomenon,” said G K Das, director (weather) at the Regional Meteorological Centre ( RMC ), Kolkata.

Clearer sky from today

Mostly associated with the rainy season, when the difference between the day and night temperature is very low, meteorologists say that even during monsoon, they have not noticed such marginal difference between the two readings.

Awell-marked low pressure over the Bay of Bengal started injecting moisture into the land as early as December 5, resulting in the minimum temperature shooting up to 20.4 °C on December 7 from the previous day’s 15.6 degrees.

Sunday’s 21.2 degrees was the highest minimum temperature the city has encountered in the second week of December in the past six years. The city has seen traces of December rainfall a few times since 2001. And it has rained more than 10mm in December at least twice in the last 10 years — in 2010, when the total monthly rainfall amount was 18.9mm, and in 2012, when December recorded a rainfall of 34.2mm. The total rainfall count this December now stands at 16.3mm, making it the third December in the last 10 years that the city got more than 10mm of rain.

“But we do not have ready records of when was the last time we had practically the same maximum and minimum temperatures in a 24-hour cycle,” a meteorologist said. According to meteorological norms, maximum temperature is the highest reading on the thermometer taken between 8.30am and 5.30pm for the days, while the minimum temperature is the lowest reading between 5.30pm and 8.30am.

The weather system that had triggered rain, a depression till Saturday evening, showed signs of weakening, transforming overnight into a less-marked low pressure by Sunday morning. “This system will get gradually weakened and we expect a clearer sky from Monday,” said H R Biswas , director (weather), RMC Kolkata.



In Video: Minimum temperature’s date with maximum on a rainy December day