The unwelcome drop in temperatures across Portugal is due to polar air sweeping south through Europe and causing a steady but determined cooling off period.
The Portuguese Institute of Sea and Atmosphere (IPMA) said there will be a drop of five to six degrees Celsius in Portugal from Monday.
The north as ever will be hit hardest with some areas hitting zero degrees by the end of the week.
"On Friday we will have minimum temperature values, especially in the northern and central regions, of around zero degrees Celsius; or one, two or three degrees below zero," according the weather service.
In the Oporto region, the minimum temperatures will be around three degrees. In Lisbon, the drop will level out at five or six degrees Celsius.
IPMA blames an anticyclone in the Atlantic which is causing the cold period.
Although the Algarve will be cooler, any frost mainly will be confined to the northern and central interior regions, plus mist, fog and weak showers turning to snow on higher ground.
The two week forecast for the Algarve shows a rise in temperatures from the 11th December with daytime temperature rising to the mid 60s Farenheit.
Until then remember, it's a lot colder ‘oop north.
