October Siliguri fog leaves all surprised

PARAG BISWAS, SNS, SILIGURI, 21 OCTOBER 21 : The dense fog that descended on Siliguri and its surrounding areas on Wednesday evening, after Darjeeling and Kalimpong districts reeled under incessant heavy rains for two days, surprised even those who saw it coming.

As the wind speeds dropped from 24 kms per hour to 11 kms per hour and minimum air temperature fell by 11 degrees from October 18 to 20, Siliguri experienced its first proper fog that lowered visibility late last evening, at least a fortnight before it was anticipated to hit.

Though it did not thankfully send air pollution levels ratcheting up considerably, the thick blanket of fog that enveloped the Siliguri sub-division after a smart shower around 8.00 pm yesterday, generated tremendous interest among residents of the subdivision, who clicked pictures and recorded videos of the fog on their smartphones and posted them on messaging apps and social media platforms. The fog also hit traffic considerably, with several people deciding not to venture out in the evening.

The signs were there on Tuesday. The wind speed, 27kms per hour on Sunday, had kept Siliguri's air quality at moderate levels, but it dropped abruptly as did the minimum temperature to 22 degree Celsius. Based on this, the meteorological experts in the town had predicted that fog would cover Siliguri and parts of the surrounding rural areas. However, it was expected only from the first week of November. What set Wednesday evenings dense fog apart from the smog that engulfs Siliguri around Diwali, and in late February and early March every year, is that the fog was caused primarily by the fall in temperature due to the torrential rains that pounded Sikkim, the Darjeeling district and the tea growing region of north Bengal, and the subsequent drop in wind speed and considerable increase in humidity, with almost no contribution of air pollutants.

The North Bengal University Weather Service Station convener, Mr Subir Sarkar told this correspondent that the October fog that occurred yesterday was very rare as the kind of rains that had lashed the region during the past 24 hours were also wry rare around this time of the year. "Weather conditions play an important role in manipulating fog and mist. The heavy rains over the past few days have cooled down the region suddenly and increased both the moisture content in the air and the water content in the soil leading to formation of fog. A high wind speed would have helped disperse the fog but a low one in the past two days has let the fog concentrate. With no strong winds to disperse them, they may linger for a few days more, but it does not indicate that winter is here and it will be more severe this year. As the sun comes out, the temperature as are most likely to soar again and the fog cover would disappear," he said.