DELHI: At 9.30am on Wednesday, an unbroken layer of fog was spread across more than 2,000km of the Indian subcontinent — starting from central Pakistan in the west, running right through the Indo-Gangetic plains and ending around Tripura. "After covering east UP and Bihar on Christmas, it started covering more areas in its west, including Delhi, by December 31. By January 2, it had covered Punjab and was continuing to move west into Pakistan. These include Agartala, Patna, Gaya, Guwahati, Gorakhpur, Allahabad, Agra, Lucknow, Varanasi, Rae Bareli, Chandigarh, Jammu, Ludhiana and Pantnagar. Fog is formed when a cold, moist air current meets relatively warm air, leading to formation of fine water droplets.

Source: Times of India January 03, 2018 20:03 UTC