Weather warning: Snow and flooding for Wales
The Met Office has issued two weather warnings of snow on Friday with up to four inches expected on higher ground in south Wales.
There are flood warnings for the lower Dee Valley in Llangollen and south Pembrokeshire. The rivers Wye, upper Severn and the Usk are on alert.
Meanwhile, trains from Cardiff to Bridgend were disrupted after lightning hit signalling equipment.
There are speed limits on the Britannia Bridge and the M48 Severn Bridge.
BBC Wales' weather forecaster Derek Brockway said: "For Thursday and on into Friday there's low pressure coming in from the Atlantic.
"It looks like we could miss the worst of the gales but we could be in for the first significant snow of the winter.
"There could be problems on the roads on Friday morning with several centimetres possible, particularly on higher ground."
The rail line between Cardiff Central and Bridgend has closed after a lightning strike hit signalling equipment.
Arriva Trains Wales said services were being diverted via the Vale of Glamorgan line through Barry with extended journey times.
Bus services have been provided for travel to Pencoed, Llanharan and Pontyclun.
The train company said they were still assessing the problem and could not say yet when the line would reopen.
Hail on motorway
South Wales Police said 10 collisions happened in the space of an hour on the M4 on Tuesday night between the Coryton junction 32 in western Cardiff and Pencoed at junction 35 during a hail storm.
The force is advising drivers to take extra care in the wet and icy conditions to prevent further accidents.
Roads Policing Inspector Jason Stroud said: "Thankfully only a handful of people involved in the incidents on the M4 last night sustained minor injuries, but it is important that drivers and cyclists remain vigilant to prevent anything serious occurring.
"It can take twice as long to stop your vehicle in rain and icy conditions, so motorists should maintain a safe distance from the vehicle ahead and ensure they are using their lights.
"The heavy rain and hail at the moment is also reducing drivers' visibility, so motorists should be extra alert.
"Allow time to de-mist and de-ice your vehicles to ensure you have 100% visibility before setting off."
He also advised drivers to ensure they had plenty of fuel in the tank, their mobiles were fully charged before setting off and to carry warm waterproof clothing, food water and a torch with them in case conditions forced them to stop en route.