The long-range forecast from the Met Office also warns that the end of January and early February have "an increased likelihood of cold weather being established across all of the United Kingdom, with temperatures continuing a downward trend to become cold or very cold".
While this is the average for January, Ms Diamond said the contrast after such a mild January will have people reaching for their warmest coats and thermals.
The average national temperature for January is 3.5C degrees.
"Colder air will move into northern Scotland later, with showers there turning increasingly wintry".
"Some drier, brighter spells are likely, perhaps with snow showers, during such spells, frost could become widespread and severe".More news: Apocalypse Now? It's 'Raining' Spiders In Brazil
Once again, Nolan forecasts, we can expect a lot of cold air coming westwards from Siberia and sweeping across Ireland.
But forecasters said the cold spell isn't down to a new "Beast from the East" - which saw wintry conditions hit the United Kingdom a year ago - and instead to "Arctic maritime airflow" coming from the north and different to the extreme weather seen in parts of central Europe.
A Met Office spokesman said: "Next week there will be colder spells and there could be a little bit of winteriness in the north, but nothing too exceptional for this time of year".
A Met Office spokesperson said there would only be a small chance of snow this week, confined to the north east of Scotland and western parts of the United Kingdom, but after that it was hard to predict.
"The week beginning Monday 21 January, there is a stronger signal of it getting colder, that would increase the risk of snow across the United Kingdom".More news: China-U.S. Trade Gap Grew to Biggest Ever in 2018
Forecasters recently warned a second Beast from the East could be on the way, after the appearance of a sudden stratospheric warming on 22 December.
When this happens in the Arctic, it can lead to a rush of cold air blowing eastwards across Europe a few weeks later.
Temperatures will plummet more than 10C from the start of the week when Atlantic winds will bring an unusually mild feel.
"This is what preceded last year's Beast from the East", said Adam Scaife, head of long-range prediction at the Met Office.More news: Canadian sentenced to death in China in drug smuggling case