Cold to get worse from December 25, says IMD forecast

Sunday was also classified as a “severe” cold day, the fifth in the past seven days, with a maximum temperature of 14.6 degrees Celsius, 7 degrees below normal, and a minimum temperature of 7.4 degrees Celsius.
The main difference between a cold day and a cold wave is that a cold day is considered when the maximum temperature or day temperature falls under a certain threshold while a cold wave is considered when the minimum or night temperature falls. The coming days could see both.(HT photos)
The main difference between a cold day and a cold wave is that a cold day is considered when the maximum temperature or day temperature falls under a certain threshold while a cold wave is considered when the minimum or night temperature falls. The coming days could see both.(HT photos)
Updated on Aug 10, 2020 01:08 AM IST
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Hindustan Times, New Delhi | ByHT Correspondent

The severe cold spell which impacted the entire northern region last week is likely to continue in the coming week with “cold wave” conditions predicted to set in over Delhi and neighbouring states after Christmas, the India Meteorological Department (IMD) said on Sunday.

Sunday was also classified as a “severe” cold day, the fifth in the past seven days, with a maximum temperature of 14.6 degrees Celsius, 7 degrees below normal, and a minimum temperature of 7.4 degrees Celsius. There was dense fog in the morning hours with less than 150 metres visibility at 5.30am and only 700 metres around 8.30am. There was, however, sunshine later in the day and chilly winds which helped disperse pollution, bringing down the air quality index (AQI) from 418 in the “severe” category to 322 in the “very poor” category.

The main difference between a cold day and a cold wave is that a cold day is considered when the maximum temperature or day temperature falls under a certain threshold while a cold wave is considered when the minimum or night temperature falls. The coming days could see both.

Also Watch l People move to night shelters in Delhi as temperature drops 

The IMD’s bulletin on Sunday said cold wave conditions are likely to develop over Punjab, Haryana, Chandigarh, Delhi and north Rajasthan on December 25. “Dense to very dense fog at a few places is very likely during morning hours over Punjab, Haryana, Chandigarh, Delhi and West Uttar Pradesh and at isolated places over East Uttar Pradesh. Besides, dense fog at isolated places will be witnessed during morning hours over north Rajasthan during next 4-5 days.” The bulletin also said cold day to severe cold day conditions are likely over Punjab, Haryana, Chandigarh and Delhi during the next 2-3 days.

“When a western disturbance moves away, there is cold air incursion from the higher reaches of northwest India. There are usually clear skies and very cold nights, the combination of these conditions brings on a cold wave,” said K Sathi Devi, head of National Weather Forecasting Centre. A feeble western disturbance has just passed which brought snowfall in the upper reaches of Himachal Pradesh, Uttarakhand and Jammu and Kashmir in the past couple of days.

“We are expecting cold wave conditions to set in over Delhi, Haryana and north Rajasthan from around December 27. But before that cold day or severe cold day conditions will continue. After 25th, we are expecting clear skies, low wind speed which will cause night time temperature to fall significantly. It is mainly because of radiational cooling when ground radiates heat away at night. The relative humidity is also high so there may be dense fog also in the morning hours,” said Kuldeep Srivastava, head, Regional Weather Forecasting Centre. At the same time, he said that before December 25, owing to relatively good wind speed and extremely cold northwesterly winds, cold to severe cold day conditions will continue.

According to the IMD, a “severe cold day” is registered when two things happen — the minimum temperature drops to less than 10 degrees Celsius and the maximum temperature is at least 6.4 degrees Celsius below normal while a “cold day” is registered when the minimum temperature is less than 10 degrees Celsius and the maximum is 4.4 degrees Celsius below normal. A cold wave is registered when a meteorological subdivision (eg: Haryana, Delhi and Chandigarh) sees a minimum temperature of less than 4.4 degrees Celsius below normal in at least two stations for two days. It will be considered a “severe cold wave” when the departure for minimum temperature is less than 6.4 degrees Celsius and the rest of the parameters are also met.

Air quality is likely to remain in the lower end of the “very poor” to “poor” category on December 23 and 24, according to the ministry of earth sciences’ air quality early warning system. The wind speed was about 15kmph on Sunday.

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Tuesday, November 30, 2021