New Delhi: December turned out to be colder than last year, and driest in seven year, despite there being just two cold days and no cold wave. A cold day is when the minimum temperature is below 10 degrees Celsius and the maximum temperature is at least 4.5 degrees below the normal. A cold wave is a condition when either the minimum temperature slips below 4 degrees Celsius or is 4.5 degrees below the season’s normal.According to India Meteorological Department, the city overall did not record cold waves this year against four in December 2021, seven in 2020, three in 2019 and eight in 2018. Similarly, there was minimal humidity this December which kept the rains away completely. December last year had four rainy days, 2020 one and 2019 and 2018, two each.The average maximum and minimum temperature for December was 23.6 degrees and 7.4 degrees Celsius against 22.4 and 8.1 last December, 23.4 and 7.1 in 2020 and 18.7 and 7.6 in 2019. In the last decade, December 2018 had been the coldest with the average minimum temperature of 6.7 degree Celsius.According to the weather analysts, the reason why this year saw a low average minimum but high daytime temperature is due to feeble western disturbances, clearer skies and low humidity. The last time when there was no cold wave in December was 2017, while there was net zero rainfall in December 2016.The weather scientists explained that the earth’s surface gets warmer during the day but the heat radiates easily to the upper atmosphere when the skies are clearer. This can cause higher daytime temperatures, but low night-time temperatures. A clouded sky, in an opposite reaction, traps the energy at night, thus lowering the night temperatures.“This year there have been more instances of clear skies and fewer foggy days,” pointed out Mahesh Palawat, vice-chairman, climate change and meteorology, Skymet. “Since the western disturbances were feeble, snow in the hills was delayed and so there were no rains on the plains. This meant the north-westerly winds did not impact the region’s daytime temperature. No rains meant low humidity and low fog.”A western disturbance is the weather phenomenon in which moisture-laden winds cause snowing in the Himalayas and rain on the northern plains. After its passage, the wind turns north-westerly, bringing cold winds from the freshly snowed areas to the northern plains.
Source: https://timesofindia.indiatimes.com/city/delhi/delhi-sees-first-december-without-cold-wave-in-4-years-driest-in-7-years/articleshow/96653099.cms