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Unseasonally early snow has swept across Wales, causing serious road problems and closing schools.

On the M4 in south Wales there were reports of a 26-mile tailback in the evening rush hour westbound from the Severn Bridge toll booths to Miskin.

Cardiff Airport also faced disruption as the runway was closed to clear away snow, but it later reopened.

Â鶹¹ÙÍøÊ×Ò³Èë¿Ú Wales meteorologist Derek Brockway said next week could see blizzard conditions on Tuesday and Wednesday.

He said the risk of this happening was between 30-40%, which made it by no means definite. But he advised people to keep an eye on the forecast, and next week will continue to be very cold.

While it was north and western parts of Wales that took the brunt of the snow earlier on Friday, heavy falls hit mid and south Wales during the afternoon.

Motorists on the M4 have been the worst affected, with stop-start traffic reported on westbound routes between the Severn crossings and up to junction 34 at Miskin.

There were long delays for drivers using the Caerphilly mountain road, and some motorists abandoned their vehicles for the night.

Cardiff Airport closed its runway at 1615 GMT on Friday as it tried to sweep snow from the runway.

It led to a flight from Dublin being diverted to Bristol, and a Malaga and Edinburgh flight re-routed to Birmingham.

The runway reopened at 1835, and passengers were advised to contact their airline, check in as normal and allow plenty of time to reachd the airport.

Flights between north and south Wales were delayed due to the weather.

The runway was closed at RAF Valley on Anglesey early on Friday due to icy conditions.

The evening flight was also affected, with passengers diverted to Gloucester and road services.

In Powys, pupils and staff at Ysgol Bro Ddyfi in Machynlleth were sent home following concerns about road conditions.

In Ceredigion, there were reports of children sheltering in a hotel on the outskirts of Aberystwyth after their bus got into difficulty.

A planned performance by the choral group Only Boys Aloud at the John Lewis store in Cardiff on Saturday was cancelled because of the conditions.

A number of councils across Wales began precautionary road gritting and most say their salt barns are full.

North Wales Fire and Rescue Service said it had attended a couple of road collisions on Friday morning.

A driver was released from a vehicle following a collision on the A543 at Denbigh. No-one was seriously hurt.

Fire crews were also called to a three-vehicle crash on the A5025 at Cemaes Bay on Anglesey.

Councils in Wales insisted that they were better placed than last year to respond to a return to wintry conditions.

Last winter it snowed every month from December through to March and some councils struggled to keep the roads clear as their rock salt supplies ran low.

In addition to what each council has, the Welsh Assembly Government has said there are 130,000 tonnes of rock salt stored for road gritting, with a further 38,000 ordered and due to be delivered shortly.

Deputy First Minister and Economy and Transport Minister Ieuan Wyn Jones said: "This will be stored in barns across the country.

"A different approach to how salt is used will also mean that it is utilised more effectively and will last longer."

An icy mountain road was closed all night after an accident involving two vehicles on Thursday evening.

Blaenllechau Road in Ferndale, Rhondda Cynon Taf, known locally as the Llanwonno mountain road, which links Ferndale and Llanwonno, was due to remain closed until 1400 GMT on Friday.

Meanwhile Welsh Water advised householders to avoid frost damage to pipes as the winter weather strikes by checking that all pipe work, cisterns and tanks in unheated areas are well insulated.

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