Delhi this week witnessed its coldest October night in 26 years with the mercury dropping to 12.5 degrees Celsius, three notches below the normal temperature, the India Meteorological Department said.
The normal minimum temperature for this time of the year is 15 to 16 degrees Celsius, the weather agency said.
According to IMD data, the national capital had recorded a minimum of 12.3 degrees Celsius on October 31, 1994. The lowest-ever October temperature recorded in Delhi is 9.4 degrees Celsius which was witnessed on October 31, 1937, Kuldeep Srivastava, the head of the regional forecasting centre of IMD, said.
For this week, the IMD forecast says the temperture will remain at least 3 degrees below normal. While the minimum tempearture on Friday is expected to be 13.1, it will drop to 11 degrees next week.
Here is IMD forecast for next seven days:
The normal minimum temperature beteween October 30-November 2 is 15.9 degrees Celsius while it is 14.8 for November 3-7.
Srivastava said the absence of cloud cover was the major reason for such low minimum temperatures this time.
Clouds trap some of the outgoing infrared radiation and radiate it back downward, warming the ground.
Another reason is calm winds which allow formation of mist and fog, Srivastava said.
The minimum temperature is likely to dip to 11 degrees Celsius by November 1, the IMD added.
Meanwhile, the air quality in Delhi inched closer to the "severe" category on Thursday, primarily due to calm winds and spike in farm fires. The Ministry of Earth Sciences' monitoring agency, SAFAR, said the share of stubble burning in Delhi''s PM2.5 pollution was 36 per cent on Thursday - the maximum so far this season.
Delhi recorded a 24-hour average air quality index (AQI) of 395. It was 297 on Wednesday, 312 on Tuesday, 353 on Monday, 349 on Sunday, 345 on Saturday and 366 on Friday.
Most of the monitoring stations, including at Shadipur (421), Patparganj (418), Bawana (453) and Mundka (427), recorded air quality in the "severe" category.
An AQI between 0 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".
A senior scientist at the India Meteorological Department (IMD) said the wind speed dipped on Wednesday which allowed accumulation of pollutants.
(With PTI inputs)