A Status Yellow fog warning is in place for Cork, Limerick, Tipperary and Waterford until Friday morning.
Met Éireann is forecasting a risk of dense fog with the warning in place from 9pm on Thursday night to 10am on Friday morning.
It is expected to remain dry overnight with variable cloud amounts and mostly light winds with some frost and fog forming where skies stay clear.
Lowest temperatures of -1 to +3 degrees Celsius are expected.
A cold start is forecast on Friday with some mist or fog patches in places.
The afternoon will be generally dry with bright spells and some isolated showers in coastal areas.
Highest temperatures of 4 to 8 degrees Celsius are expected.