Northern Railways, in a statement, said that some of the trains have been cancelled and several are running well behind schedule due to dense fog.
Cold wave conditions prevailed at a few places over eastern region and many places over western parts of the state in the past 24 hours, a MeT official said.
Night temperatures appreciably fell in Varanasi, Faizabad, Bareilly, Meerut divisions and changed a little in the remaining parts of the state.
They were markedly below normal in Faizabad, Kanpur, Lucknow, Meerut divisions and appreciably below normal in Varanasi, Allahabad, Bareilly, Moradabad and Agra divisions.
MeT department predicted that fog would occur at many places over the state.