Gutsy north westerly winds were blowing across the state on Tuesday, pulling down day temperatures further.
Temperatures were near sub-zero in Muzaffarnagar at 0.7 degrees.
Owing to the unrelenting cold weather, the government has ordered closure of all schools till Jan 12, after which a call would be taken again, Basudev Yadav, director (Primary Education), told IANS.
Regional MeT department director JP Gupta said the cold wave would persist for another week though foggy conditions would not stay for long.
Due to fog in some parts, vehicular and rail traffic were crippled.
Flights at the Chowdhary Charan Singh international airport in Lucknow and Babatpur airport in Varanasi were delayed.
More than a dozen trains were running late from and to Lucknow, railway officials said.