Western disturbance is an extratropical storm that originates from Mediterranean sea towards Himalayas carrying heavy moisture over northern India.
Day time temperatures above 20 degree Celsius, night time temperatures in the comfortable range of 7-10 degree Celsius, little or no rainfall and clear skies on most days. Winter in much of north India this time around has been characterised by pleasant, spring like conditions and based on on-going trends, we may have already seen winter peak. The milder or warmer than usual winter across most states in north India, with the exception Jammu and Kashmir and parts of Himachal Pradesh, has been seen due to feeble western disturbances or weather systems that are trigger cold spells and rainfall, experts said.
Western disturbance is an extratropical storm that originates from Mediterranean sea towards Himalayas carrying heavy moisture over northern India. They are responsible for cold waves across the northern plains and rainfall too. Meteorologists and independent scientists have said that the weak western disturbances coupled with the effects of the biggest El Nino in the last two decades has caused warmer conditions this winter.
"We have witnessed pronounced effects of global warming in the last two decades caused by greenhouse gas emissions and urbanisation and the warm winter is also perhaps another manifestation of the warming. The temperatures during winter have routinely been above normal and will continue to be so. In addition, there is warming of the Pacific Ocean, a fallout of the El Nino phenomenon," said DS Pai, director, long-range forecasting division, India Meteorological Department (IMD), Pune.
El Nino is a weather phenomenon that wherein there is warming of central and eastern Pacific Ocean and it has been established that these conditions cause droughts in south Asia, extremely heavy rainfall in South America and other such extreme weather events in different parts of the world. Last year, El Nino caused a below par monsoon in the sub-continent and scientists believe that it will be continue beyond summer of 2016.
In this warmer than usual winter, the temperatures have been consistently high. The Delhi-National Capital Region saw an average minimum temperature of 9 degree Celsius in December, almost 0.6 degrees higher than usual, said GP Sharma, vice-president, meteorology, Skymet weather services. Similarly, maximum temperatures have been routinely five to six degrees above normal hovering around 25-26 degree Celsius against the average of 18-20 degree Celsius.
It was not only the temperature that was affected but rainfall too took a hit. Winter rainfall, crucial for the Rabi crop across the northern plains was meager. In December, with the exception of Himachal Pradesh and J&K, all northern states recorded scanty rainfall with a deficit of 75-80 per cent. In January, the situation has worsened as till now, rainfall has been next to none in all northern states except Himachal Pradesh and J&K.
"We have almost crossed the halfway mark in winter and the northern plains have received little rainfall. There are no appreciable chilly winds and rainfall is possible only after a week," Sharma added.
Meanwhile, the IMD has said that there is little hope of a drastic drop in temperatures in the coming weeks. "A western disturbance is approaching J&K and once that passes over, temperatures will drop slightly. It is unlikely that temperatures will see a big drop and rainfall too will be sparse," said BP Yadav, head, National Weather Forecasting Centre.
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