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Weatherman on the ball this winter

Game-changer: The Alipore Met office has three such high-capacity servers, key players in the code-breaking process. (Bishwarup Dutta)

The forecast was an unbelievable four-degree rise in the next two days when Calcutta shivered at 12.5 degrees Celsius, the second coldest February 3 in a decade. Believe it or not, the minimum temperature was 16.2 on February 5.

On January 26, the minimum climbed to 15.3 but the Met office predicted a dip of one degree for each of the next two days. As if on cue, the minimum read 14 on January 27 and 13 degrees the next day.

The Celsius behaved like a rodeo bull this winter, bucking under “normal” for a couple of days and swooshing up to fall again.

But the Alipore weather office was on the button with its forecasts almost every time the slippery mercury dipped or rose and buried for good an enduring joke: “Who does everyone listen to but never believe? The weatherman!”

Barring a couple of misses, a combination of highly advanced gear and latest forecasting techniques ensured that the 139-year-old India Meteorological Department was spot-on with its forecast.

Science, not sorcery, involving intricate charts and computers helped meteorologists crack the weather code.

“We consider weather parameters such as temperature, pressure and wind at a point of time at locations surrounding a given place and try to predict the weather,” said B.K. Bandopadhyay, the deputy director general of IMD, Delhi.

Minute-by-minute data for a vast area and collected from land, sea and space (satellites) stations were analysed to arrive at accurate predictions.

Here’s how it is done

■ For Calcutta forecasts, data from manned weather stations within a 16,000sqkm radius is considered and fed into supercomputers

■ Printers produce giant charts from this data for manual reading. These are fed into a set of computers for analysis

■ For each of about 1,000 locations, the charts depict pressure, temperature, relative humidity, wind speed, etc.

■ Data also comes from unmanned or automatic stations in sea buoys and on ships

■ More charts are produced with data from weather balloons released from stations across the world to record parameters at different levels of the atmosphere

■ Readings and pictures of clouds come from satellites like Kalpana-1

The Regional Met Office, Alipore, got a made-in-France computer in 2010 for “numeric weather prediction”.

Called Synergie, the computing system displays real-time animation of weather features such as temperature, pressure and wind.

Conditions can be studied at the click of a button till the last moment before the forecast is finally issued.

G.C. Debnath, the director of IMD Calcutta, said 27 automatic weather stations in Bengal and more than 80 in neighbouring Bihar, Odisha and Jharkhand have been added over the past few the years. “Data from these stations, as well as 440 manned stations across the country, have helped us make accurate calculations,” he said.

Bandopadhyay agreed: “The new stations (125 unmanned ones in the past 4-5 years across India) are ensuring accurate forecasts.”

The transition from the primitive manual system to new-age computing took some time. “Your understanding of a software becomes better over time,” Debnath said. The necessary chemistry between man and machine has now been reached, he added.

The improved understanding was put to test by a yo-yo winter as unusual fluctuations left half the city wheezing. In January, there were 10 occasions when the minimum temperature oscillated on either side of “normal”.

The IMD hit bullseye on most occasions. “But predictions can go wrong when a weather system develops suddenly and rapidly, such as the late-summer Norwesterlies,” said Debnath.