Snowfall of up to 30cm (12in) is forecast for some areas, with about 5cm (2in) expected more widely.

A Wales-wide warning for snow is in place between 12:00 GMT on Saturday and 23:59 GMT on Sunday.

The Met Office has also issued a yellow warning for ice from 16:00 on New Year’s Day until 10:00 on Thursday, while flood alerts apply to some parts of the country.

The forecaster said there was a “fair bit of uncertainty” over how long the snow would last, but warned power cuts and travel delays were possible and urged people to prepare in advance for adverse conditions.

It said Wales was one of the areas most at risk of disruption – along with north England and the Midlands – with high ground to be hardest hit and drifting possible due to strong winds.

It comes after wind gusts of up to 75mph (120km/h) were predicted across Wales on New Year’s Day and another yellow weather warning issued.

On New Year’s Day, Natural Resources Wales urged people not to travel to its forests and reserves due to high winds.

The A487 from Machynlleth, Gwynedd to Furnace, Ceredigion, was closed on Wednesday afternoon due to flooding.

A tree blocking the railway at Llanwrtyd, Powys, meant trains between Swansea and Shrewsbury could be cancelled or revised, Transport for Wales said, adding other services may also be disrupted due to weather.

A suspected landslip on the A470 between Dolgellau and Mallwyd in Gwynedd caused some traffic delays, as well as flooding on the A494 at Pont Lliw near Llanuwchllyn, which has since receded and the road fully reopened.

At about 08:00, firefighters were called to the B5106 near Llanrwst, Conwy county where a vehicle had driven into flood water and become stuck.

The two rescued occupants were cold but unharmed, the fire service said.

Both the B5106 and the A470 were partially closed through the county as well, with flood water blocking the former near Maenan and the latter shut south of Dolgarrog.

Holyhead on Anglesey was originally due to reopen on 20 December, but the port said Terminal 3 and Terminal 5 ferry berths will need to remain closed to prioritise safety.

The prolonged closure follows two incidents affecting the Terminal 3 berth on 6 and 7 December, resulting in part of the structure collapsing, which the port said made it unusable.

The port has apologised for the disruption on the main sea route between north Wales and Dublin in Ireland, but said it was still assessing the full extent of the damage.

It follows uncertainty as to whether the port would reopen before Christmas, and the Irish prime minister Taoiseach Simon Harris said on Monday it was “highly unlikely”.

However, the Welsh government had said on Monday that it remained hopeful it would open by 20 December.

Stena Line and Irish Ferries each operate four daily ferry sailings travelling each way between Holyhead and Dublin.

On average, two million passengers use Holyhead a year and about 1,200 lorries and trailers make the crossing every day.

The closure had already led Ireland’s national postal service to abandon plans to use Holyhead for Christmas deliveries.

President of the Irish Road Haulage Association, Ger Hyland, said he was not surprised by the ongoing closure, but it continues to be “detrimental” to its members and the Irish and Welsh economies.

“We’re now travelling hundreds of miles more, paying higher ferry costs because of a lack of available routes,” said Mr Hyland.

“It’s meaning a huge commercial cost to the industry which won’t be seen until after Christmas,” he added.

Stena line apologised for the inconvenience caused and said it was doing all it could to mitigate the effects of the closure.

In a statement, the ferry operators said it was offering sailings from Dublin to its ports in Birkenhead, Fishguard and Heysham, as well as additional sailings from Belfast to Cairnryan to assist the flow of trade and passengers.

Managing director of haulage company BM Transport, Darren Murphy, said they would typically ship 75 to 120 loads a day through Holyhead but are having to run at half of its capacity.

The company is based in Monaghan, in Ireland, but also has a depot in Mona in Holyhead, and Mr Murphy says he is concerned it’s going to become an “absolute nightmare” going into January.

“I’d say nobody seems to have a solution and neither the Irish government or the Welsh government have come up with any sort of increase capacity,” Mr Murphy added.

In a joint statement, the Welsh and Irish government said it was “pressing on at pace” with contingency plans in a coordinated effort between itself, the Port Authority, Stena Line, Irish Ferries, and Isle of Anglesey council.

In a statement, it added: “We will continue to work together in the short term to ensure passengers and freight get through, and in the longer term to preserve the resilience and success of the Port of Holyhead, which is so important to both our nations.”

The closure of the port comes after Storm Darragh battered the UK with gusts up to 93mph (150km/h).

The high speed winds caused damage to Terminals 3 and 5, and the port said underwater inspections to begin remedial works were delayed to Tuesday, 10 December, once Storm Darragh had passed.