The weekend saw another February temperature record fall, with Wales surpassing the record of 18.6c which had stood since 1990.
A high pressure region is forecast to bring unseasonably warm weather to other parts of the continent, with large parts of western Europe expected to see temperatures in the high teens over the coming days. Previously, the highest recorded temperature in February had been 19.7C in London in 1998.
It is the first time temperatures have exceed 20C during winter, according to a Met Office official.
It's reached 20.3 °C at Trawsgoed, Ceredigion making it the UK's warmest February day on record.
And just after 1pm in Trawsgoed, history was made when the thermometer reached 20C - the first time it has ever happened in winter since records began.
The further the air travels over land the more moisture it loses and faster it heats up, the Met Office said.
But forecasters say temperatures should be back to normal as there is a risk the sunshine might disappear behind thick cloud.
They said rain and strong winds could potentially affect the northwest at times.
The unheard-of sizzling winter temperatures are said to be a result of the Foehn Effect.
Temperatures across Wales reached 18C (64.4F) in many places on Sunday, though it is unlikely to break the United Kingdom record for February, when the mercury soared to 19.7C (67.46F) in Greenwich in 1998.
Exactly a year ago, the highest temperature recorded across Northern Ireland was 7.8C at Magilligan in Derry.