Despite clear skies and lots of sunshine, the minimum temperature remained close to four degrees Celsius in most parts of the national capital on Thursday, according to the India Meteorological Department (IMD).

The Safdarjung Observatory, which provides representative data for the city, recorded a minimum temperature of 4.6 degrees Celsius as frosty winds from the western Himalayas continued to sweep across Delhi.

The Ayanagar and Ridge weather stations recorded minimum temperatures of 3.8 degrees Celsius and 3.5 degrees Celsius, respectively.

The maximum temperature is likely to settle around 18 degrees Celsius, the IMD said, predicting 'cold day' conditions at a few places.

The IMD had declared a cold wave in Delhi on Tuesday as icy winds blowing from snow-covered western Himalayas brought the minimum temperature down to 4.1 degrees Celsius, the lowest in the city this season so far.

According to the IMD, the minimum temperature is likely to remain around five degrees Celsius till Friday.

Kuldeep Srivastava, the head of the IMD's regional forecasting centre, said the western Himalayas recorded widespread snowfall due to strong western disturbances and now frosty winds have been blowing towards the plains, bringing the mercury down.

For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal for two consecutive days.

"However, for small areas such as Delhi, a cold wave can be declared if the criteria is fulfilled even for a day," Srivastava said.

A "cold day" is when the minimum temperature is less than 10 degrees Celsius and the maximum is 4.4 degrees Celsius below normal.

The air quality was recorded in the "poor" category.

The city's air quality index (AQI) was 248 at 11 am. The 24-hour average AQI was 262 on Wednesday and 230 on Tuesday.

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".