LUCKNOW, Dec. 18 -- The India Meteorological Department (IMD) on Wednesday issued red and orange alerts, warning of dense to very dense fog and cold conditions in several districts of Uttar Pradesh over the next three days, till December 20. As a thick layer of fog enveloped large parts of the state, day temperatures dropped by 5 to 10 degrees Celsius in many districts. In view of the cold and foggy weather, the Lucknow district administration revised school timings with effect from Thursday. Classes 1 to 12 in all government and private schools across all boards will start at 9 am or later till further orders, district magistrate Vishak G said. According to the IMD, the presence of an inversion layer in the lower troposphere caused extensive fog cover across the state for most of the day. As a result, maximum temperatures on Wednesday fell by 5 to 6 degrees Celsius in several areas and by 8 to 10 degrees in some pockets. However, there was no significant change in minimum temperatures. On Wednesday, Bareilly saw zero visibility, while visibility in Lucknow dropped to around 50 metres in the early hours. Bareilly recorded the lowest maximum temperature at 13.4 degrees Celsius, which was eight notches below normal. Shahjahanpur recorded 13.8 degrees Celsius, Muzaffarnagar 15.2 degrees Celsius, Ayodhya and Najibabad 16 degrees Celsius each, and Sultanpur 16.8 degrees Celsius. In Lucknow, the maximum and minimum temperatures were recorded at 17 degrees Celsius and 10 degrees Celsius, respectively. The forecast for Thursday indicates a mainly clear sky, with dense fog likely during the early morning hours. Day and night temperatures are expected to hover around 20 degrees Celsius and 10 degrees Celsius, respectively. Among minimum temperatures recorded on Wednesday, Kanpur was the coldest at 6 degrees Celsius, followed by Etawah at 7 degrees Celsius, Bulandshahr at 8 degrees Celsius, Lakhimpur Kheri at 8.2 degrees Celsius and Hardoi at 8.5 degrees Celsius. The red alert for dense fog was issued for 20 districts, including Deoria, Gorakhpur, Sant Kabir Nagar, Basti, Kushinagar, Maharajganj, Siddharthnagar, Gonda, Balrampur, Shravasti, Bahraich, Lakhimpur Kheri, Sitapur, Barabanki, Bijnor, Moradabad, Rampur, Bareilly, Pilibhit and Shahjahanpur. An orange alert was issued for Hardoi, Ayodhya, Amroha, Sambhal and Badaun....