A cold wave gripped Delhi on Tuesday as the 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, the India Meteorological Department (IMD) said.

The maximum temperature also dipped to 18.5 degrees Celsius, more than four notches below normal, the weather department said.

At 4.1 degrees Celsius, the minimum temperature at Safdarjung Observatory, which provides representative data for the city, was five notches below normal on Tuesday morning.

At Jafarpur, the mercury dipped to 3.6 degrees Celsius.

The Ayanagar and Lodhi Road weather stations recorded a minimum of 4 degrees Celsius and 4.2 degrees Celsius, respectively, the IMD said.

Last year, the minimum temperature had dropped below the five-degree mark in the last week of December.

According to the IMD, the mercury is set to dip further. The minimum temperature is likely to settle around 3 degrees Celsius on Wednesday and is likely to remain below 5 degrees Celsius till Friday.

Kuldeep Srivastava, the head of the IMD’s regional forecasting centre, said the national capital witnessed both “cold wave” and “cold day” on Tuesday.

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.

Both “cold day” and “cold wave” conditions are predicted in parts of Delhi from Wednesday to Saturday, Srivastava said.

The air quality was recorded in the “poor” category.

The city’s 24-hour average air quality index (AQI) was 230. It was 160 on Monday, 305 on Sunday and 356 on Saturday.

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”.