New Delhi, Dec 17 (IANS): The national capital on Thursday recorded the lowest minimum temperature of the season so far with the mercury dipping to 3.5 degrees Celsius. The India Meteorological Department (IMD) has forecast the cold wave will persist till Friday.

"Ridge observatory has recorded the minimum temperature of 3.5 degrees Celsius. The cold wave condition will persist till December 18, following which the temperature will rise up a notch," said head of the IMD's regional forecasting centre, Kuldeep Srivastava.

The weather scientist further said that the icy winds are blowing towards the national capital region from the snow-clad mountains of Jammu and Kashmir and Himachal, which witnessed heavy snowfall on December 12.

The temperature remained close to 4 degrees Celsius in most parts of the city despite ample sunshine and clear skies.

Besides Ridge, the Safdarjung Observatory, which provides the representative data, recorded a minimum temperature of 4.6 degrees Celsius, while Ayanagar, Lodhi road and Palam Observatory recorded it at 3.8, 4.2 and 4.5 degrees Celsius.

On Tuesday, the weather department had declared a cold wave when the minimum temperature plummeted to 4.1 degrees Celsius. It saw a massive dip of 10 degrees in two days -- from 11.4 degrees Celsius on Monday and 14.4 degrees on Sunday.

Delhi's air quality remained in the "poor" category due to favorable wind speed. The city's air quality index (AQI) was 250 at noon. It expected to gradually deteriorate to very poor category by Sunday.

"The cold day conditions are likely in the region and high surface winds are forecasted for the next 48 hours and likely to slow down after that," said System of Air Quality and Weather Forecasting and Research.

It added, "The AQI is forecast to stay in moderate to poor category on December 18, poor category on December 19 and likely to deteriorate to the lower end of very poor on December 20."