A tropical air mass from across the Atlantic could bring temperatures of up to 14C to parts of the UK over the next week.
Following ice warnings over the last weekend, an area of high pressure is due to bring "relatively benign conditions," according to forecasters.
They said the UK will be largely dry and brighter on Monday, though a cold and frosty night is predicted for much of England and Wales.
"Last week, we had places struggling to get over 0C, this week we could see temperatures get up to 14C if the sun can get through the fog," Met Office forecaster Ollie Claydon told The Independent.
"Certainly as we get through the fog we are looking at double figures quite widely."
However, Mr Claydon warned the UK will face more severe weather tonight, with the potential for a fog warning to be put in place overnight.
"Large parts of central and southern England could see fog tonight," he said. "In patches that could linger into Tuesday morning and through the afternoon."
The fog could potentially bring travel disruption across the UK.
The Met Office said road traffic could be slowed down and advised people to take extra care in low visibility.
The rest of the week is expected to be drier, brighter and cooler in the north, and cloudy and mild in the south.
