LUCKNOW, Dec. 19 -- A thick blanket of dense to very dense fog brought much of Uttar Pradesh to a near standstill on Thursday, prompting the India Meteorological Department (IMD) to issue red and orange alerts for several districts and warn of cold to severe cold day conditions over the next two to three days, officials said. The IMD's meteorological centre in Lucknow said fog intensified due to an inversion layer in the lower atmosphere, an anti-cyclonic circulation over western and adjoining central India, and the influence of a tropical westerly jet stream over north India. These conditions caused persistent daytime fog and a fall in maximum temperatures across many areas over the past 48 hours. "The prevailing conditions are likely to continue till at least December 20, with several districts witnessing cold to severe cold day situations," said Md Danish, a senior scientist at the Lucknow meteorological office. Extremely dense fog, with visibility dropping below 50 metres, was recorded at Agra, Bareilly, Kanpur, Prayagraj, Gorakhpur and Kushinagar air force stations. Aligarh reported visibility of about 40 metres, while Ballia, Bahraich and Hardoi witnessed near-zero visibility. Dense fog was also reported from Moradabad, Ayodhya, Varanasi, Basti and Azamgarh, while Lucknow airport recorded moderate fog with visibility around 200 metres. The IMD warned that eastern and central districts, including Prayagraj, Varanasi, Jaunpur, Ghazipur, Azamgarh, Mau, Ballia, Deoria and Kushinagar, may face severe cold day conditions, while parts of western and central UP are likely to experience cold day conditions....