Temperatures could drop to around -7C in some areas overnight as the recent cold snap continues.
Met Éireann said it be very cold today with frost and ice clearing slowly in some areas and with highest temperatures of 4C.
The forecaster said it will be bitterly cold tonight with lowest temperatures of at least -5C and possibly colder in some parts of the country.
Scattered wintry showers of hail, sleet or snow will affect eastern and southeastern counties and it will be coldest in Connacht and Ulster.
The frost and ice will persist tomorrow and temperatures will remain below or near freezing in parts of the midlands and west.
On Thursday morning, rain, sleet and snow will continue to move southwards and will clear in the afternoon with sunny spells and some wintry showers in Ulster and Connacht and daytime temperatures of just 2-4C.
The cold weather will continue into Friday with a widespread severe frost on Friday night and lowest temperatures of around -4C.
Cold today with frost or ice slowly clearing. Cloudiest in Leinster and Munster, with scattered wintry showers of rain, hail, sleet and snow. Drier and brighter elsewhere. Highs of just 1 to 4 degrees. https://t.co/9gKN6SVok4 pic.twitter.com/EOe13nznej— Met Éireann (@MetEireann) January 5, 2021
Head of Forecasting at Met Éireann Evelyn Cusack said that from now until Sunday, there will be some very cold weather, with Friday a bitterly cold night with air temperatures of -5C to -7C and ground temperatures down to below -10C.
She said while major roads will be gritted, minor roads and surfaces could freezing over.
Wicklow Roads Policing Unit were on patrol near the Wicklow Gap and the Sally Gap this morning when they took these pictures. Road conditions are very poor and the Sally Gap remain impassable. #holdfirm #staysafe pic.twitter.com/UkDZoLoHn4— Garda Info (@gardainfo) January 5, 2021
Ms Cusack said that while there will be snow flurries in the east, the greatest chance of snow will be during tonight and tomorrow morning, when a cold front will move down along Ireland, bringing a band of rain, sleet and snow.
Meanwhile, the RSA said a number of driving tests were cancelled this morning due to icy conditions on roads in the midlands, west and northwest.