A status yellow weather warning for snow and ice will remain in place across the country until Friday afternoon.
Met Éireann updated its forecast at 1pm after a previous warning for the northwest expired at 10am.
Heavy showers are expected in the north and northwest on Thursday night with some snow likely to fall. The forecaster also warned of a slight risk of thunder.
AA Roadwatch are advising drivers to avoid the M7 Dublin to Limerick road between junctions 22 and 24 after two collisions on the motorway where conditions are very wet.
Gardaí are reporting snowy and slippery conditions on the Letterkenny/Ramelton Road and on the N13 Ballybofey/Letterkenny Road at Lurgybrack due to snow and sleet. Motorists are advised to avoid the area.
Hundreds of schools were closed in Northern Ireland on Thursday where the heaviest snow has fallen.
Temperatures are set to drop below zero once again overnight before rising to highs of between 3 and 7 degrees on Friday. Frost and icy patches will set in on Friday night with lowest temperatures of minus 2 degrees in store.
Saturday will start off mainly dry and cold with frost and ice for a time in the north and east, but mild weather is on its way from the south bringing with it rising temperatures.
Sunday will start off wet in most areas and temperatures will reach 12 degrees in gusty westerly winds. The forecast suggests the mild, unsettled weather will remain into next week.
Met Éireann forecaster Evelyn Cusack has defended her organisation's method of classifying storms and issuing warnings.
Storm Fionn
She was responding to criticism from Channel 4 forecaster Liam Dutton who claimed that Storm Fionn earlier this week should not have been termed a storm.
Ms Cusack, who is also chairwoman of the European Task Team for Storm Naming, told Newstalk Breakfast that she could understand Liam Dutton’s point of view
On Twitter he had said: "This is the problem with the storm naming system. The Irish Met Office, @MetEireann, have different (lower) criteria that are numerically driven, compared to the @metoffice's impact-based criteria. How can something be a joint initiative when each use different criteria?!"
Ms Cusack pointed out that Storm Fionn was not a traditional swirling vortex storm and that Met Éireann had issued the storm warning because of the risk of high seas and dangerous conditions on Ireland’s west coast.
“There have been tragic deaths involving people swept off rocks and cliffs. Conditions can be very dangerous,” she said.
“I don’t think you can say we were being too cautious. The conditions we predicted did occur.”
Mr Dutton followed up his original critical tweet with this comment: “#StormFionn that has been named by @MetEireann shouldn’t have been named. It needs no more than a standard weather warning. It’s not even a low pressure with a storm centre, just a squeeze in the isobars. What next? Naming raindrops? It’s ridiculous!”
Ms Cusack said that although Storm Fionn was not a traditional storm it did fulfil Met Éireann’s criteria and she was certain that people on the streets had experienced storm force winds.
