The run-up to Christmas is forecast to begin with a cold spell, prompting concern some people may break the rules over meeting family and friends indoors.
The weather looks like turning from fine for many on Sunday - barring a few showers in the South and West - to bleak.
On Monday 21 December, rain and strong winds are expected in many central and southern parts, with showers in the North.
The rain will continue on and off into Wednesday - when the UK-wide "Christmas bubbles" policy begins.
Up to three households can then mix exclusively over a five-day period, but Scotland and Wales have advised a more cautious approach to the size and duration of gatherings.
From 23 December, it's set to be fine - but cold, with overnight frost and freezing fog patches.
"There'll be just a few showers in the North and West, which will turn wintry, especially over the hills," said Sky News weather producer Chris England.
"So not wonderful for outdoor meeting at first, and chilly thereafter, although mainly dry."
There is concern it could cause some people to potentially break or stretch the rules on indoor gatherings.
The virus can spread easier indoors due to poorer ventilation and confined space.
Professor Bobby Duffy, director of the Policy Institute at King's College London, told Sky News that research found bad weather making it hard to meet loved ones was the top reason people gave for finding the rules harder to follow.
"With temperatures dropping and the number of daylight hours declining, opportunities to socialise in gardens or parks over Christmas will be even more limited, and the temptation for some to break the 'three-household bubble' rule and see others indoors may increase," he explained.
"But those who do so are likely to be in the minority - 82% of people said they're being just as, or even more, careful about obeying the restrictions than they were during the UK-wide lockdown earlier in the year."
Polling by Savanta/ComRes also found 11-15% of people said they might break the Christmas rules, though 80% plan to comply.
Chris Hopkins, associate director at the polling company, warned: "The danger is that the public may not end up following the rules as closely as they currently claim.
"If this is the case, and coronavirus cases spike more than expected once the leftover turkey has been eaten, a lengthy lockdown at the start of 2021 could anger the sizeable numbers who would have accepted much tougher measures over Christmas."