An orange weather warning is in place for Co Clare.
Met Éireann issued the fog warning on Friday evening and predict it to last until 9am on Saturday morning.
Widespread fog will be dense in many places overnight with conditions already dense on the N18 between Bunratty and Cratloe. There is also a risk of freezing fog.
All over Ireland the orange fog weather warning is in place. Lowest temperatures are forecast to be between -2 and -6 degrees. Frost and fog returned quickly on Friday evening with the frost to become severe in some locations which will result in icy roads. Drivers and pedestrians are urged to take care in light of the weather warning.