Scotland is worst affected by the snow and ice alert which kicked in just after midnight on Thursday.
It affects Central, Tayside and Fife, the Highlands and the former Strathclyde area and is schedule to last the whole day until 11.55pm.
Met Office forecasters predict frequent showers will push across north west Scotland falling as snow above 200m.
They also say 10-20cm of snow could be possible over the highest routes in parts of northern Argyll, Lochaber, Wester Ross and Easter Ross.
Forecaster Marco Petagna said: “There will be wintry showers throughout the day on Thursday and pretty strong winds.
“They will fall as snow above 200m.”
Strong winds are also forecast which forecasters say could lead to some drifting and temporary blizzard conditions.
At lower levels showers are more likely to fall as a mixture of rain, sleet and hail potentially washing off any treatment with surfaces turning icy, particularly overnight.
An ice warning is also in place for Northern Ireland which kicks in at the same time and lasts until 10am.
Experts predict the areas affected will be Antrim, Londonderry, Fermanagh, Tyrone, Armagh and County Down.
Mr Petagna added: “There will certainly be some wintry showers in the province, although it’s an ice warning that is in place for Northern Ireland.
“Even into Friday there’s a few showers to come. it’s wintry turning to sleet in western areas.
“There’s quite a split between west and east.”