New Delhi, Dec 22 (PTI) A layer of dense fog enveloped the Indo-Gangetic plains including Delhi Thursday morning, affecting road and rail traffic.

A railway spokesperson said 20 trains were running late by 1:30 to 4:30 hours.

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According to the India Meteorological Department (IMD) 'very dense' fog is when visibility is between 0 and 50 metres, 51 and 200 is 'dense', 201 and 500 'moderate', and 501 and 1,000 'shallow'.

The Met office said the Palam and Safdarjung airport logged visibility levels of 200 metres at 5:30 am.

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On Tuesday, visibility levels had plunged to 50 metres at both these places. South westerly winds at the middle tropospheric level and a consequent increase in temperatures had led to some improvement on Wednesday.

Amid low temperatures, high moisture and still winds, a layer of dense to very dense fog persisted over Punjab, Haryana, northwest Rajasthan, west and east Uttar Pradesh and Bihar.

"Satellite imagery shows continuation of dense fog layer from Punjab and northwest Rajasthan to Bihar," an IMD official said.

At 5:30 am, visibility levels stood at zero in Bhatinda; 25m in Ganganagar, Chandigarh, Gorakhpur and Bareilly, and 50m in Amritsar, Churu Bahraich and Ambala.

Visibility levels are likely to improve from Wednesday night/Thursday morning due to decrease in relative humidity at the lower tropospheric level over the Indo-Gangetic plains, the IMD said.

(The above story is verified and authored by Press Trust of India (PTI) staff. PTI, India’s premier news agency, employs more than 400 journalists and 500 stringers to cover almost every district and small town in India.. The views appearing in the above post do not reflect the opinions of LatestLY)