The national capital witnessed another "severe" cold day on Thursday and is likely to record its longest cold spell in December after 1992 as temperatures are predicted to drop further, the weather department said.
The city recorded a low of 5.8 degrees Celsius and a high of 13.4 degrees Celsius on, seven notches below normal. Humidity levels shot up to 100 per cent.
A severe cold day and a moderate fog is predicted on Friday. A cold wave is likely to grip the national capital on the weekend as the mercury is predicted to drop to 4 degrees Celsius, the MeT department said.
Since December 14, most parts of the city have witnessed 13 consecutive "cold days" or a 13-day "cold spell". The last time such a long cold spell was witnessed was in December 1997.
The national capital recorded the maximum of 17 cold days in December, 1997.
According to Kuldeep Srivastava, head of the India Meteorological Department's regional forecasting centre, a "cold day" is when the maximum temperature is at least 4.5 notches below normal.
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A "severe cold day" is when the maximum temperature is at least 6.5 degrees Celsius below normal, he said.
The air quality in the city was recorded in the very poor category (349) at 4 pm.
It is forecast to touch the severe category by Saturday night as "very calm surface winds, low mixing layer, dense fog and high humidity are expected for the next five days starting December 27".
The regional forecasting centre of the IMD maintains data since 1992.