Isolated cold day conditions expected in Delhi as air quality improves

Isolated cold day conditions were expected in Delhi on Wednesday, as a shallow fog enveloped the region, the air quality improved to the “poor” zone, and the minimum temperature was two degrees above normal at 8.6°C.

A 24-hour rolling average Air Quality Index (AQI) of 300 (poor) was recorded at 9am, compared to 310 (very poor) at 4pm on Tuesday. The AQI was expected to be “very poor” until Friday.

On Tuesday, Safdarjung, Delhi’s representative weather observatory, recorded a maximum temperature of 15.7°C, three degrees below normal, and Palam 13°C. At least two stations logged cold day conditions on Tuesday as the mercury plunged to 7.6°C.

A “cold day” is when the minimum temperature is below 10°C and its departure from normal is 4.5°C or more. It is a “severe cold day” when the maximum is 6.5°C or more below normal.

The shallow fog, mainly at the upper levels, on Wednesday plunged the visibility to around 800 metres at Palam and Safdarjung.

Upper-level fog and cloud cover typically raise the minimum temperatures but bring down the maximum. They keep conditions frigid in a narrow window between the maximum and minimum.

Delhi recorded the lowest maximum temperature of 14.2°C in six years on December 31. On December 30, 2019, the maximum temperature dropped to 9.4°C, making it the coldest December day in 119 years.

The mercury was expected to dip further until January 15. Weatherman Navdeep Dahiya said single-digit maximum temperatures were expected across the region. “For Delhi, we can expect the maximum to fall and be in the range of 12-15°C at Safdarjung in the next nine to 10 days or so. It may be between 10-14°C at Palam. The minimum may not fall like 2019, but it should still fall to a range between three and four degrees C,” Dahiya said.

He added that early morning fog will persist in the mid-and-upper levels during the day.

The India Meteorological Department did not forecast cold day conditions on Tuesday. Dahiya said a combination of fog and icy-cold northwesterly winds made it feel extremely cold during the day. “Despite fog, which keeps the minimum high, these icy-cold winds will not only keep the maximum low, but also gradually bring the minimum lower.”