Heavy fog gave way to "exceptionally mild" weather on Saturday, with unseasonably warm conditions likely to continue for much of the week before conditions worsen considerably.
"Temperatures could reach 16C or 17C today," Marco Petagna, a meteorologist at the Met Office said.
"It has been warmer for a while now but this is exceptionally mild for the time of year."
Although the day will be sunny for many, some cloud and rain is forecast over Northern Ireland which could push into Scotland and Cumbria.
The Met Office predicts a "mild, dry and bright afternoon with sunny spells" for most of the UK.
The warmest temperatures are expected in north Wales and in parts of Scotland.
"The Moray coast should do particularly well," Mr Petagna said.
"Temperatures will be down a little on Sunday. 15C or 16C, but it will still be warm."
The day is forecast to be dry, bright and sunny, with some wind in northern regions.
Settled conditions are likely to continue into next week for southeastern parts of the UK but rain and strong winds will affect the northwest.
"Temperatures may gradually become closer to normal. Any spells of rain will tend to weaken as they move southeast, just bringing cloudier skies," a spokesperson for the Met Office said.
The warmer weather, while pleasant, is not here to stay.
Colder weather will return as Atlantic fronts cross the UK, bringing unsettled conditions, strong winds and rain in early March.
