The forecaster says it will be very cold with wintry weather
A status orange snow and ice warning has been issued for a number of places.
The alert for Cavan, Monaghan, Donegal, Leitrim, Mayo and Sligo is in place until 6.00pm Friday.
This is an upgrade of a similar alert issued Tuesday.
The forecaster says it will be very cold, with wintry weather from Wednesday evening onwards until Friday night.
There will be showers of hail, sleet and snow - with moderate accumulations to lower levels inland, and more significant amounts on high ground.
There is also a risk of drifting and blizzard conditions at times, and some scattered thunderstorms.
While a status yellow snow and ice warning remains in place for Munster, Leinster, Galway and Roscommon.
This will bring showers of hail, sleet and snow, with some accumulations to lower levels - but especially over high ground.
Showers will be more scattered in south Leinster and along the east coast of Leinster, with icy conditions.
Met Éireann has also issued a status yellow weather advisory for the entire country.
It says showers will turn wintry in many places from Wednesday evening, with falls of sleet and snow expected.
The heaviest of the snow fall is most likely over Ulster, Connacht, north Leinster and west Munster and especially on high ground.
While the Road Safety Authority (RSA) is advising all road users to take extra care when using the roads over the next 72 hours.
It says low temperatures will mean roads may be icy.
The RSA is asking road users to check local weather and traffic conditions, and be aware of the conditions before making a trip.
It is advising motorists to clear windows and mirrors before setting out, carry a screen scraper and de-icer.
It is asking people to not use hot water on windscreens, as this can crack the glass.