New Delhi: The India Meteorological Department (IMD) has issued an “orange alert” warning for Delhi on Monday, saying that the national capital may witness “dense” to “very dense” fog that could reduce visibility to as low as 200 metres in many parts of the city and surrounding areas. The low visibility in Delhi-NCR is expected to disrupt road, rail, and air traffic on November 18. Earlier, a warning of delay in flight operations at the Delhi airport was issued by aircraft carrier IndiGo and the airport authority.

An IMD official, on Sunday, confirmed, “There are chances of dense to very dense fog in Delhi on Monday, with smog expected later in the day.” The alert comes as the national capital experiences one of its foggiest days of the season.

The IMD forecast for Monday predicts that the fog and smog will affect airports, highways, and railway routes, leading to difficult driving conditions and slower travel times across the region.

Impacts on Road, Rail, Flight Operations

According to Delhi Airport officials, Indira Gandhi International Airport (IGI) is equipped with advanced landing systems, including the CAT-3 Instrument Landing System (ILS), which allows flights to land even when visibility is as low as 50 metres. However, the system cannot support take-offs if visibility is below 125 metres. In case the fog at the Delhi airport is dense or very dense, then it could cause significant flight delays.

Earlier, on November 13, Delhi recorded its first “very dense” fog of the season, causing more than 550 flight delays, according to flight tracking site Flightradar24. The next day, despite slightly improved visibility (400 metres), delays continued, with over 350 flights affected.

The fog condition in Delhi appeared to be irregular on Sunday with varied visibility in various parts of the city. On Sunday, Palam Airport recorded 500 metres between 8.30 am and 9:00 am, while at Safdarjung Airport visibility dipped to 300 metres at 7.00 am.

The visibility remained poor throughout the day on Sunday as the sun’s rays failed to penetrate the fog. This resulted in the peak of the poor visibility at 900 metres at Palam in the evening and 800 metres at Safdarjung. Notably, the visibility on Saturday was as good as 2,200 metres during the day.

The dense fog is also expected to cause delays on the roads and railways. The train services may be impacted due to reduced visibility, while speed limits on roads also be kept under check to ensure road safety.

How Dense Fog Evaluated

IMD classifies fog based on visibility levels:

• Shallow fog: Visibility between 500-1,000 metres
• Moderate fog: Visibility between 200-500 metres
• Dense fog: Visibility between 50-200 metres
• Very dense fog: Visibility of 50 metres or less

Fog is defined as reduced visibility (below 1,000 metres) with relative humidity above 75%. If humidity is lower than 75%, it is considered smog.

Amidst dense fog conditions, the IMD has advised residents of Delhi to take extra precautions while travelling and to stay updated on weather conditions throughout the day.