Forecasters say bitter overnight lows of Minus 12C in the Highlands means there is not enough time for temperatures to recover by day.
As a result, Aviemore will remain at Minus 4C at lunch time today . Warnings for up to eight inches of snow on higher ground – sparking possible power cuts - mean that official alerts for severe weather now extend into eight consecutive days.
The only crumb of comfort in the upcoming forecast is that Scotland stands the “best chance” for a White Christmas.
Tom Morgan of the Met Office said: “Large areas of Scotland will not rise above freezing during the day as we go through this week.
“Night time temperatures are so low, there is not enough time for temperatures to recover due to the shorter daylight hours.
“A low of Minus 4C is possible even in lowland areas of Scotland on Monday.
“Sunday night or Monday night will probably register the lowest temperatures of this spell, anything between Minus 10 and Minus 12C .
“It will be fractionally less cold at night as we go through the rest of the week, as wind increases and we start to see more in the way of cloud cover.
“However, warnings are in place for significant falls of snow right up to Thursday and we expect Shetland to see substantial snowfall on Monday into Tuesday. There will be some disruption in the Northern Isles, even for those hardy folk.”
A 48-hour-long warning for snow kicks in at noon tomorrow for the north, north east and Western Isles. Between six and eight inches of snow (15-20cm) is predicted for higher spots, leading to travel difficulties and falls on icy surfaces.
The Central Belt will see nothing disruptive, with no more than a few flakes for Glasgow and Edinburgh.
Mr Morgan held out the mounting prospect of a White Christmas, though it is by no means certain.
He said: ”There is a chance of a White Christmas but we are two weeks out and forecasting snow can be very tricky. However, I’d say Scotland has a greater chance of snow lying this year, compared to average Christmas Days.”