More snow is expected today following yesterday's falls in Northern Ireland and in parts of the Republic, particularly in the midlands, the west and the north-west.
In Northern Ireland, forecasters are predicting further snowfalls and sub-zero conditions for today and tomorrow before milder conditions return before the weekend.
Meanwhile, Met Éireann expects more snow showers and temperatures ranging from 2 to 5 degrees in the Republic today. Rain, sleet and widespread frost are also forecast.
A man was killed in a car accident which happened in icy conditions at about 6. 10 a.m. yesterday.
Mr Liam Fagan's car was involved in a head-on collision with a truck at Feed Cross, near Drumad, Co Louth.
Mr Fagan (24) was from Priorland, Dublin Road, Dundalk, Co Louth.
The driver of the truck was treated for minor injuries at Daisy Hill Hospital in Newry.
Gardaí in Dundalk have appealed for witnesses to the accident to contact them at 042-938 8400. The road was closed for a time yesterday morning and traffic was diverted around the Cooley peninsula via Omeath.
In Northern Ireland, rail, ferry and road services were affected and there was criticism by politicians on all sides of preventive measures taken by the roads services.
Flights into the Belfast airports were also hit and there were fresh delays following those experienced last week when the London airports were snow-affected.
The Glenshane Pass, which rises to about 1,000 ft on the main Belfast-Derry road, was closed for a time and there were further road closures around Carrickfergus, Co Antrim.
Gritting operations were hampered following a security alert. The Spelga Pass which crosses the Mourne mountains in Co Down was also badly affected.
The rail line to Larne, Co Antrim was subject to delays as was the link from Coleraine, Co Derry to Portrush, Co Antrim. There were also difficulties on the service from Belfast to Bangor, Co Down.
Translink, the company which runs public transport, reported a largely operational but delayed bus service in Belfast and across Northern Ireland.
Commuters travelling by car experienced severe delays yesterday morning.
There were tailbacks up to eight miles long on the M1 into Belfast. There were several minor accidents around the back roads in the Dublin area yesterday. A three-car pile-up caused long tailbacks at Clonee on the Meath/Dublin border yesterday morning.
The main Belfast-Larne road saw three-mile jams in each direction as lorries en-route to the port got into difficulties.
Stena called off its high-speed ferry services from Belfast to Scotland.
Met Éireann had expected widespread frost, rain and sleet overnight, particularly in the north of the country.
Icy patches are expected this morning, and AA Roadwatch has advised motorists to avoid back roads today and to take extra care.
Mr Jim O'Brien of Met Éireann said the cold spell was expected to begin to ease tomorrow. Cloud and rain would gather, he said, and conditions would become milder.
This was not the first cold spell of the winter, Mr O'Brien said, but it was the first significant fall of snow.