Met Éireann has issued a status yellow weather alert, warning of snow and ice on Thursday.
Up to 3cm of snow is forecast for most of the country, with larger accumulations possible on higher ground.
The snow is forecast to arrive in the southwest first, with the warning in place from 7am.
It is then expected to travel north across the country, with much of Leinster, Connacht and Ulster forecast to receive snow showers from around 4pm.
The southeast - counties Wexford, Carlow, Kilkenny, Waterford and Cork - are not covered by the Status Yellow warning.
It will be in place until 6am on Friday.
The RSA have advised all road users to take care when using the roads, with slippery conditions expected.
Temperatures tonight are forecast to reach as low as -4, meaning roads and paths may be icy and as a result people are warned to beware of black ice.
Hill walkers and climbers are being asked to exercise extreme caution during the cold snap.
Day Three of the Christmas Festival at Leopardstown Racecourse in south Dublin will be subject to an early morning inspection due to the weather.