A status yellow rainfall weather warning has been issued for several counties.
The alert - in place for Carlow, Kildare, Kilkenny, Laois, Wicklow, Offaly and Tipperary - runs until 2.00am on Thursday.
Met Éireann says a spell of heavy rain is likely to lead to some spot flooding, which will turn to sleet and snow in places on Wednesday.
Thursday night will see most places dry, but showers will persist about north Connacht and west Ulster - and along the east Leinster coast.
Minimum temperatures of -1 to +2°C with frost forming.
There will also be moderate north to northwest winds, still fresh to strong and gusty near coasts.
On Friday it will be a sunny day for most after a cold, crisp start.
But there will be cloudy periods with the risk of showers near the east coast.
Maximum temperatures here of 6 to 9°C in light to moderate north to northwest winds - gusty near the east coast.
Clear spells and light northerly or variable breezes will allow temperatures to fall to between 1 and -3°C on Friday night - with a sharp ground frost inland and the risk of icy patches.
There will also be a few patches of mist.