A blanket of dense fog took the national capital by surprise on Wednesday morning, reducing visibility and affecting flight operations, even as the maximum temperature remained above normal — as it has been over the past 21 days in what has been a warmer-than-usual February.
On Tuesday, the India Meteorological Department (IMD)’s forecast had spoken of the likelihood of partly cloudy skies for Wednesday, and had not mentioned any possibility of fog.
Officials on Wednesday said the occurrence was a combination of several factors — a dip in night temperature from the previous day, clear skies, and a western disturbance moving away from the region.
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“When the day and night temperature was high, evaporation was higher. The winds were also calm. With the night temperature falling by 2 to 3 degrees and the prevalence of clear skies, radiation-type dense fog formed today,” said IMD scientist RK Jenamani. Radiation fog develops on account of calm winds and western disturbances, resulting in localised fog formation, he added.
Further, a western disturbance moving away from the region resulted in the creation of an induced cyclonic circulation in Haryana due to which moisture was prevalent in the atmosphere that aided fog formation. “Dense fog in various regions was mainly due to the dip in temperature due to the passage of the western disturbance, away from the region. The presence of induced cyclonic circulation at the lower level also accumulated moisture in the atmosphere,” said Jenamani.
The maximum temperature in Delhi stood at 29.3°C on Wednesday, five degrees above normal, and nearly two degrees below Tuesday’s reading of 31.4°C. The minimum temperature on Wednesday stood at 14.6°C, three degrees above the normal temperature for this time of the year, but less than Tuesday’s reading of 16.1°C.
The temperature has remained above normal for most part of February, so far. On Monday, Delhi’s maximum temperature shot up to 33.6°C , the highest recorded since 2006.
Both IMD’s Safdarjung observatory, which is representational of Delhi’s weather, and Palam weather station, recorded a visibility of 50 metres at 8.30am. Airport officials said that 27 flights due to land in Delhi were diverted to Jaipur, Amritsar, Lucknow, and Varanasi due to low visibility between 6.30am and 10.30am.
According to IMD’s weekly forecast, the maximum temperature is expected to hover around 29°C on Thursday while the minimum may touch 13°C, and the day is likely to witness a mainly clear sky with shallow fog in the morning. According to IMD’s seven-day forecast, the day temperature will hover in the 29-31°C range till the end of this week while the minimum is expected to be between 13°C and 15°C in the next few days.
Hardeep Kaur, a teacher at a school in Vasant Kunj, said she was surprised when she spotted a dense layer of fog while leaving for work. “When I opened my door in the morning, I saw dense fog. I haven’t seen denser fog than today for the most part of winter. As I proceeded to my workplace in Vasant Kunj, the fog got denser,” said Kaur.
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The fog also impacted Delhi’s air quality, which slipped into the “very poor” zone on Wednesday. The city logged an air quality index (AQI) of 302, according to the Central Pollution Control Board’s (CPCB) 4pm bulletin. On Tuesday, AQI was in the “poor” zone with a reading of 245. An AQI between zero and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor”, and 401 and 500 “severe”.
According to the Early Warning System (EWS) for Delhi-NCR developed by the Indian Institute of Tropical Meteorology that CAQM (Commission for Air Quality Management in National Capital Region and Adjoining Areas) relies on for its forecasts, the air quality is likely to improve on Thursday. “The air quality may improve significantly and reach the poor category on Thursday. The air quality is likely to remain in the poor category on Friday and Saturday,” said the CAQM forecast.