Motorists are being advised to take special care on the roads today and tomorrow as storm-force winds and overnight frost bring a pre-Christmas chill to the country.
About 4,000 homes in the west of the country are without power due to a lightning storm this afternoon, ESB Networks said.
North Mayo was worst affected but crews have now restored power to most of west Galway.
Repair crews were also working to restore power to homes on Inis Mór.
What Met Éireann described as a "vigorous" Atlantic storm was due to bring overnight winds of up to 130 km/h last night, creating a heightened risk of debris on the roads earlier.
The strong winds are due to spread east, followed by overnight frost, thus increasingly the possibility of a white Christmas at least on higher ground.
The Road Safety Authority cited a risk of vehicles veering across the road today to avoid debris, while drivers might not have full control of vehicles in strong winds.
High-sided vehicles, motorcyclists and cyclists are particularly vulnerable to strong winds, the authority said.
In Galway, high tides forced the city council to close a section of exposed coastal road at Salthill until Thursday, with local access only.
About 50 Garda checkpoints will be in place across the western region this week to test for speeding, drink or “drug” driving.
AA Roadwatch reported spot flooding on roads in Dublin, Wexford and Cork and in some rural areas yesterday. It said particular caution is needed in sheltered areas and on higher ground.
It has been snowing heavily around Cavan town and particular care is needed on secondary routes.
Snow was sticking to higher ground around Bailieborough.
In Monaghan, snow was sticking in the Carrickroe and Corcaghan areas, AA Roadwatch said.
There were also very poor conditons in Offaly, especially on the Bannagher to Birr road (R439).
Sleet and rain are causing poor driving conditions. Gardaí were also dealing with a crash along this route near Bannagher.
In Meath there were very strong cross winds on the M3 Dublin to Cavan road at Dunboyne.
Extreme care was required between Dunshaughlin and Navan due to a lot of excess surface water and strong cross winds, AA Roadwatch said.
In Salthill, Co Galway, Dr Colohan Rd is closed from the jct with Grattan Rd to Seapoint because of expected stormy conditions and the possibility of flooding. The road is expected to reopen on St Stephen’s Day.
Irish Ferries cancelled its Swift ferry services between Dublin and Holyhead yesterday and today with all passengers transferring to the cruise service.
Among utility companies affected by the storm was eircom which said it has committed all available resources to work through the Christmas period to repair customer faults. Lightning and high winds have caused widespread structural damage to polls and cables as well as damage to customer’s in-home wiring.
Christmas Day is expected to be crisp and dry but another storm is approaching Ireland on Friday, Met Éireann warned. On the odds of a white Christmas, it said temperatures would be as low as -2 degrees in the early hours of tomorrow, with the possibility of a dusting of snow on higher ground.