Snow and ice are expected to cause travel chaos as many people head back to work after the Christmas holiday.
Heavy snow is expected in some areas and below-freezing temperatures are forecast, so there are warnings that roads may be icy.
Tom Tobler, a forecaster with MeteoGroup, the weather division of the Press Association, said mid Wales is expected to see the worst of the snow on Monday.
"There could be quite a substantial amount over high ground," he said, predicting there could be as much as 30cm by the time the band of snow passes.
The Midlands could also see snow later on Tuesday, he added. "There could be several centimetres in places, enough to cause some problems."
Overnight temperatures could fall as low as minus 15C in parts of Scotland and minus 5C in the north of England.
The Met Office issued severe weather warnings for heavy snow overnight in Grampian, Orkney and Shetland, Highlands and Eilean Siar.
It also has warnings of icy roads across much of Scotland and in north east England, the Yorkshire and Humber region and eastern parts of Northern Ireland.
Heavy rain is expected in the South of England although it could turn to sleet over high ground.
The forecast follows a spell of snow, sleet and ice which has gripped the UK for more than a week but relented in most parts over recent days.