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Nip in air back with rain on radar

A cyclonic circulation near Gujarat is threatening to bring rain to Calcutta over the weekend and add a wag to the winter’s tail.

A cold wave in north India has played its part in reviving a semblance of winter in the city just when everyone was bracing for summer.

If rain comes as expected, the atmosphere will be rid of water vapour, paving the way for the return of cold winds from the north. The chill may not last long but it should still warm the cockles of the Calcuttan’s heart that longs for an extended winter.

The Celsius has plunged across the country after more than a week of prematurely warm weather that had led people to believe that the chill had gone for good this season.

Thursday’s maximum temperature of 28.3 degrees Celsius and the minimum of 16.3 degrees were both a notch below normal. In Mumbai and Ahmedabad, the maximum temperature was two to three degrees below normal. In the east, Patna and Ranchi shivered as the Celsius dropped to seven and nine degrees respectively.

Delhi, in the north, logged a maximum temperature of five degrees below normal and a minimum reading of two notches below normal. Cold winds from central Asia have contributed to the dip in temperature.

A senior scientist with the India Meteorological Department in Delhi said the fall was “well within the normal deviations observed at this time of the year”.

“We haven’t seen any significant drop in temperatures, except at a few places in the northern Indian plains,” said Basab Bandopadhyay, deputy director-general of forecasting services at the IMD. “But the fall in temperature is within normal departures during winter.”

Weather scientists said the cold wave in northern India started in the aftermath of the withdrawal of a western disturbance. A cold wave is declared when the minimum temperature in any place dips five degrees or more below normal in winter.

In the western states, the fall in day temperature has been just as pronounced because of the cyclonic circulation, which is leading to cloud formation and blocking out the sun.

Calcutta experienced a strong breeze on Thursday that triggered a sharp drop in the minimum temperature from 17.6 to 16.3 degrees overnight.

The impact of the change in weather was, of course, more than what the Celsius indicated because of the warm phase that preceded it. Five days ago, on Sunday, the maximum temperature in Calcutta was 32.2 degrees, five notches above normal. The minimum reading that day was 19.7, four degrees above normal.

Friday might see the temperature rise a bit with the approach of the cyclonic circulation from Gujarat, but rainfall over the weekend should do the trick. “All things remaining the same, the resultant chill would stay for a few days,” a weather scientist said.

Saturday afternoon is the earliest that the rain is tipped to start. It had last rained in Calcutta 76 days ago, on October 26, when 157mm of rain was recorded in 24 hours.

The forecast for the weekend is “moderate” rain between 7.6mm and 35.5mm, just enough to have a bearing on the Celsius without making Calcuttans wish the weather was warm rather than cold and blustery!

“The cyclonic circulation that is travelling east is at the lower levels of the atmosphere. This height is ideal for the formation of rain-bearing clouds. So we expect moderate rainfall,” a Met official said.

The Met department has also predicted that the cold wave in north India will continue till the first couple of days of next week.

Experts said it was a coincidence that the cold wave and the cyclonic circulation had occurred at the same time, creating conditions that would allow winter to sign off from eastern India in style. “Thanks to the current cold wave in the north, chilly winds will rush in as soon as the atmosphere in the east sheds excess moisture,” the Met official said.

This winter has seen more variance than a chameleon changes colours. In the span of barely 72 hours, Calcutta had graduated from the second coldest February 3 in a decade to the warmest day in almost three months.

Count on the Celsius to spring one last surprise, if not more, this weekend.