Visibility down to zero in several parts of Delhi as ‘very dense’ fog engulfs city

Dense to very dense fog engulfed the national capital in the early hours of Friday as visibility dipped to zero for over four hours between 5am and 9am. More than 50 flights were delayed at Delhi’s Indira Gandhi International airport, while at least 20 trains were running late by an hour or more, officials aware of the matter said.

Moisture from western disturbances that brought rainfall to large parts of the plains over the last two days have led to the ‘very dense’ foggy conditions, the India Meteorological Department (IMD) said, with similar weather expected till Saturday.

Another western disturbance is expected to influence the plains of northwest India from Saturday evening, with the possibility of drizzles in parts of Delhi, the IMD said.

“There is plenty of moisture in the atmosphere due to the western disturbance that has just passed Delhi NCR. With winds calming, this has allowed very dense fog to form again in the region,” an IMD official said on Friday.

The IMD classifies it as ‘shallow’ fog when visibility is between 500m and 1,000m, as ‘moderate’ when the visibility stays between 200m and 500m, as ‘dense’ when visibility is between 50m and 200m, and ‘very dense’ when the visibility drops below 50m.

Meanwhile, the minimum temperature settled at 7.0°C on Friday, a notch below normal; it was 12.3°C on Thursday. The maximum is forecast to be around 19°C today, with the sun expected to be out after 12 noon.

Delhi is currently experiencing its worst foggy spell in recent years. Data shared by the IMD earlier this week showed the months of December and January recorded a combined 128 hours of dense fog – visibility below 200m, making it Delhi’s worst spell since the winters of 2014-15, when 174 such hours were recorded.

In January 2024 alone, there have been 14 days (88 hours) of dense fog, the data revealed. This was the highest since 2015 (98 hours), the IMD said.

February, however, has begun on a wet note, with the capital recording 27.1mm of rainfall till 8.30am today morning. This is already higher than the entire month’s long period average (LPA) of 21.3mm.

As a result, Delhi witnessed its cleanest air quality in over three months, with the average air quality index (AQI) returning to ‘moderate’ once again. The average AQI was 177 (moderate) at 9am on Friday. It was 178 (moderate) at 4pm on Thursday.

The last time Delhi’s air was ‘moderate’ was on October 20 (195) and October 19 (121).

Forecasts by the Early Warning System (EWS) for Delhi – a model under the ministry of earth sciences – said Delhi’s air should remain ‘moderate’ in the first week of February.

“Delhi’s air quality is likely to be in the ‘moderate’ category from February 2 till February 4. The outlook for the subsequent six days also shows air quality is likely to be in the moderate category,” the EWS said in its bulletin on Thursday.