New Delhi was enveloped in a thick blanket of fog on Thursday morning, severely disrupting visibility and daily life. The India Meteorological Department (IMD) recorded a significant plunge in visibility, prompting it to sound a yellow alert for more foggy days ahead.
Visibility Plummets, Disruption Begins
The fog began intensifying in the early hours. At 2:30 am, visibility was recorded at 300 metres at Safdarjung, the city's base weather station, and 500 metres at Palam. The situation deteriorated rapidly as the morning progressed. By 6 am, it had dropped to 200 metres at Safdarjung and 150 metres at Palam. The worst was recorded at 6:30 am, when visibility plunged to just 100 metres at both locations. Conditions only started improving after 7:30 am.
This marked the season's second day of dense fog, though its intensity was slightly less than on Monday, December 15, when visibility remained below 200 metres for several consecutive hours.
IMD Scientist Explains the Cause
IMD scientist Krishna Kumar provided insights into the meteorological factors behind the dense fog. He explained that a change in wind direction to easterly on December 13 led to visibility dipping to 200 metres on December 14. "Due to enhanced moisture, the visibility dropped to 0 metres on Dec 15, leading to a massive disruption," Kumar stated. The fog layer thinned on December 16 due to strong winds over the city.
Kumar detailed that the dense fog initially formed over northern parts of Uttar Pradesh on Wednesday and subsequently moved southwards towards Delhi. "As winds slowed down, it led to the dense fog formation in the city. Visibility dipped to 100 metres despite north-westerly winds," he said. He added that the period from mid-December to January is climatologically the most suitable for dense fog formation in the region.
Yellow Alert and Temperature Dip
The IMD has issued a yellow alert, warning of moderate to dense fog on Friday, Sunday, and Monday. Dense fog is likely at isolated places in the early morning hours on these days. Saturday morning is expected to see shallow to moderate fog. The department classifies fog intensity based on visibility:
- Very Dense Fog: Visibility under 50 metres
- Dense Fog: Visibility between 50-200 metres
- Moderate Fog: Visibility between 200-500 metres
- Shallow Fog: Visibility between 500-1,000 metres
The fog and overcast skies also impacted temperatures. Thursday's maximum temperature settled at 20.1 degrees Celsius, which is two degrees below the seasonal normal and a significant 4.6 degrees lower than Wednesday's maximum. The minimum temperature was 9 degrees Celsius, one degree above normal.
Kumar also mentioned that a western disturbance is expected to affect Delhi until December 23. Under its influence, heavy rain is likely in Jammu and Kashmir on December 21, with moderate fog in Himachal Pradesh. Delhi is likely to experience continued cloudiness.
