A new warning has been given to drivers in parts of Wales as freezing weather continues to affect travel and sport.
There was heavy fog on the second Severn Crossing and Monday's 1000 GMT Stena Line Holyhead to Dun Laoghaire ferry was cancelled.
The cold weather also saw the Ospreys-Scarlets sell-out Boxing Day derby and Monday's Newport Gwent Dragons-Cardiff Blues derby postponed.
Meanwhile, retailers reported busy Boxing Day sales.
The St David's shopping centre in Cardiff estimated that 150,000 shoppers went through its doors on Sunday.
Steven Madeley, the centre director, said: "As Boxing Day fell on a Sunday this year, trading hours were shorter than normal but there was still the demand from shoppers demonstrated by the fact that one of our car parks was full before the stores even opened at 11am.
"We expect Monday and Tuesday of this week to be extremely busy."
Frozen pipes at the Liberty Stadium meant the Ospreys-Scarlets game was called off. A crowd of more than 20,000 was expected for the Magners League fixture, and a rescheduled date has yet to be fixed.
A frozen pitch forced Monday's Newport Gwent Dragons and Cardiff Blues to be postponed.
The A470 southbound between Abercynon and Pontypridd was partially blocked due to a broken down car, and motorists were warned of icy roads in the Swansea area in particular.
Meanwhile, 12,000 tonnes of grit from Sweden are expected in the next few days to replenish low stocks.
When the new grit arrives, it will be distributed to local authorities.
It was ordered by the Welsh Local Government Association, which earlier this week warned of dwindling stocks.
Meanwhile, rail users were reminded that no Valley Lines services are expected to run on Monday due to a strike by Arriva Trains Wales drivers.
The strike was announced after drivers voted for industrial action in a row over pay and conditions.
Arriva Train Wales has apologised for the inconvenience to passengers and said they planned to run a full service on all other routes on the network on Monday.
Forecasters said the weather will remain dry across Wales for the rest of Sunday, and while still cold, less so than recently.
The Met Office warned that any freezing fog would be slow to clear with outbreaks of sleet and snow across Wales leading to some icy stretches.
On Monday, outbreaks of rain and hill snow are forecast, mainly in the west but spreading east later.
The cancellation of Monday's Newport Gwent Dragons game against Cardiff Blues was described as bitterly disappointing by Mark Jones, stadium manager at Rodney Parade.
"The staff have worked really hard this week to try and ensure that tomorrow's game will go ahead but we have been beaten by extraordinary weather conditions," he said.
He added his thanks to supporters who offered to help clear the pitch of snow.
The match will be played at a later date to be scheduled by Celtic Rugby in conjunction with both teams.