Drivers have been warned to take care as Met Éireann has issued a status yellow fog warning for Leinster, Cavan and Monaghan on Thursday morning.
Dense freezing fog, frost and icy patches are widespread, affecting areas in the west of the country as well as those under the Met Éireann warning.
AA Roadwatch is reporting black ice around Sligo town, Drumcliffe and Ballintogher as well as Castlebar and the N26 Ballina to Foxford road.
Carrick-on-Shannon and Manorhamilton are also experiencing bad fog and icy patches.
A car was reported to be travelling the wrong way in thick fog on the M9 dual carriageway near the Carlow South junction.
AA Roadwatch is advising drivers to slow down, use fog lights in affected areas and to turn them off when no longer needed.
The weather warning is due to expire at 11am, with fog expected to clear giving sunny spells and light rain along the west coast.
Highest temperatures will be between 4 to 8 degrees, dropping to a low of -2 on Thursday night.
