Cold wave grips Delhi, mercury plunges to 2.2 degrees C at Ayanagar, Ridge

A cold wave gripped the capital with Ayanagar and Ridge weather stations recording a minimum of 2.2 and that in Safdarjung 3 degrees Celsius on Thursday as “very dense” fog enveloping the city delayed flights amid visibility of as low as 25 metres at Palam.

Safdarjung is Delhi’s base weather station, where the previous lowest this season was 4.4 degrees on Wednesday. Other parts of Delhi have recorded a minimum of as low as 2.2 degrees.

On January 1, 2021, Safdarjung station recorded a minimum temperature of 1.1 degrees Celsius, the lowest also in the last decade. The all-time lowest (0.6 degrees Celsius) was recorded on January 16, 1935.

The Ridge weather station earlier on December 25 recorded the lowest temperature this season for any station at 3 degrees Celsius.

The India Meteorological Department (IMD) said the cold wave conditions will continue until Friday. A cold wave is declared in the region when the minimum temperature is 4.5 degrees or more below the normal mark, or when it drops to 4 degrees or lower.

The very dense fog delayed flights in the early hours. In a tweet, the Delhi airport said low visibility procedures measures for making landing easier when visibility dips below 800 metres were in place. “All flight operations are presently normal. Passengers are requested to contact the airline concerned for updated flight information,” the airport tweeted at 6:15am.

The IMD classifies fog as shallow when visibility dips below 1000 metres. Moderate fog is when the visibility is between 200 and 500 metres. Dense fog is declared when the visibility is below 200 metres and very dense when it is below 50 metres.

Under the low visibility procedures, the most basic set of precautions is put in place to guide pilots in landing under CAT-I. Only flights and pilots who are CAT-II compliant are allowed to land when visibility is under 550 metres. CAT-III A pilots can land when visibility is between 175 and 300 metres. CAT-III B is the most stringent qualification for a pilot to land a flight, allowing landing even when visibility is 50 metres.

Flights can land at the airport when visibility is 50 metres. No flights are allowed to depart unless the runway visibility range is 125 metres, leading to flight delays.

An Air Quality Index (AQI) of 339 (very poor) was recorded at 7am compared to 343 (very poor) at 4pm on Wednesday. Delhi’s air quality showed some improvement on Wednesday, dropping down to the lower end of the very poor category.

This prompted the Commission for Air Quality Management in NCR and Adjoining Areas to revoke all measures under Stage-III or the severe category of the Graded Response Action Plan.

The revocation allowed the resumption of private construction, the reopening of brick kilns and hot mix plants not operating on clean fuels, etc.

Early Warning System’s forecast for Delhi showed Delhi’s AQI was likely to remain in the very poor category till January 13.

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 over 400 severe.