'Cold day': Delhi records lowest maximum temperature of the season

Delhi recorded a "cold day" on Thursday as the maximum temperature dropped to 15.2 degrees Celsius, seven notches below normal and the lowest so far this season, the India Meteorological Department (IMD) 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 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 the national capital.

Ayanagar and Ridge weather stations recorded a low of 3.8 degrees Celsius and 3.5 degrees Celsius.

The Palam weather station recorded the lowest day temperature of 13.2 degrees Celsius -- nine notches below normal.

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

For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or lower, and 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 are fulfilled even for a day," Srivastava said.

The air quality in the national capital was recorded in the "poor" category on Thursday.

The city's 24-hour average air quality index (AQI) was 256. It 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".