LUCKNOW, Dec. 17 -- 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 ex...