Met Éireann has issued a status orange weather alert amid widespread dense fog and icy patches.
The national forecaster says to expect poor visibility, especially in midland and eastern areas. The warning is in place until 11am.
The fog is set to clear throughout the morning, with a low cloud forming in some areas for a time.
There's fog in many parts of the country. Use fog lights when needed but switch them off when no longer necessary. http://t.co/qvBPcggiUy
— AA Roadwatch (@aaroadwatch) March 18, 2015
The forecast says to expect some sunny spells as the afternoon moves on. Some areas will remain hazy or misty and highest temperatures are predicted to be between 9 and 13 degrees.
The average temperature will dip to between minus 2 and 2 degrees on Wednesday night and the fog is expected to return, especially in western and southern areas.