Commuters will wake up to frost on Monday morning as temperatures plummet across the country.
Northern Ireland, Scotland and northern England will all face slippery road conditions with likely transport disruptions during Monday's rush hour while snow is set to sweep Scotland.
But by Wednesday, milder temperatures will return with a mixture of sunny spells and showers for the rest of the week.
Met Office spokeswoman Helen Roberts said: "It is going to be a colder night on Sunday than we have had of late with cool air filtering in from the west.
"So we will see a return of frost on Monday, which we haven't had in a while."
"With showers blowing through overnight, we have ice risks in most northern areas," she added.
Ms Roberts said the main risk will be on untreated surfaces, so pavements and roads which have not been gritted.
⚠️ Yellow Weather Warnings issued ⚠️
Ice and Snow across Northwestern parts of Scotland
all day Monday 0000 - 2359
Ice across the rest of Scotland, Northern Ireland and parts of Northern England tonight
Latest info 👉 https://t.co/QwDLMfRBfs
Stay #WeatherAware pic.twitter.com/WQ4eVMlTjR— Met Office (@metoffice)January 26, 2020
She said people should leave extra time for their journeys, take extra caution on roads and keep an eye on the latest Met Office updates.
"It is going to be slippery surfaces with the potential for transport disruptions, mainly on trains and roads," she added.
The combined ice and snow warning for northwest Scotland will be in place for the whole day until midnight on Tuesday.
"We have showers spreading in from the sea and they will be wintry above 100m," she said.
"We will continue to see these showers throughout the day, so there could be an accumulation of snow across the highlands."
Monday and Tuesday will see temperatures reaching highs of around 5-6C in the north and 8-9C in the south.
Tuesday could see temperatures fall to -2-3C in Scotland, according to the Met Office.
It is likely there will be further warnings issued for Monday night into Tuesday as Brits face a second bracingly cold night with temperatures dropping below freezing, Ms Roberts said.
But Wednesday will bring milder temperatures as the mercury rises back up towards 11C in the south and 9C in the north.
"Wednesday onwards, we start to see a return of some milder air and quite a changeable second half of the week," Ms Roberts said.