Temperatures could go as low as minus 6 tonight, with widespread frost and icy stretches forecast.
There's a national low temperature alert in place until 12pm tomorrow, while the northwest has a status yellow warning for snow.
Met Éireann said most places will stay dry with clear spells and patches of fog and freezing fog.
A spokesperson for the national forecaster said: "However, some sleet and snow showers will feed into southwestern, western and northern areas. Lowest temperatures of -6 to -1 degrees in a light northwest breeze."
Speaking on RTÉ, Carlow Weather's Alan O'Reilly said: "“It will be very hard frost again tonight and very little thaw tomorrow, with a hard frost again overnight on Thursday and very little thaw again... it will stay bitterly cold."
