Mild December and early January weather is set to yield to a blast of icy cold conditions and gale force winds in parts of the country.
Met Éireann has issued a "status yellow" weather warning and says there may be snow on high ground by Wednesday.
A yellow alert is to notify those who are at risk because of their location and/or activity, and to allow them to take preventative action. Such warnings are for weather conditions that do not pose an immediate threat to the general population.
The national forecasting service said it would be mild at first on Tuesday night with a little rain or drizzle in places. It will get windy and colder later in the night, however, with clear spells and showers developing.
Some of the showers will turn wintry on northern hills late in the night.
Lowest temperatures will be 3 to 6 degrees. Strong and gusty westerly winds will develop overnight and will be up to gale force in northern and northwestern areas.
Wednesday will be cold, windy and blustery with bright or sunny spells and showers. The heaviest and most frequent of these will be over Ulster, said Met Éireann.
Westerly winds will continue fresh to strong and gusty, with gales on northern coasts.
Scattered showers on Atlantic coasts will move further inland overnight on Wednesday and turn “increasingly wintry”, with snow on higher ground, the meteorological service said.
Temperatures will reach a low of -1 to +2 degrees.
South Munster may see sleety rain and snow later. Thursday will also be a very cold day, with the risk of sleety rain and snow affecting the far south of the country for a time. It will be brighter elsewhere with wintry showers of hail, sleet and snow, mostly across Connacht and Ulster.
Wintry showers will continue in the west and north through Thursday night, with widespread frost and ice.
A wind warning is in place for Donegal, Leitrim, Mayo and Sligo until Wednesday at 10am.
The cold weather advisory remains in place until Saturday afternoon.
Minister for Transport Shane Ross asked people to be "winter ready" and to take all necessary precautions ahead of the cold snap.
“I would urge all people to heed the advice of the agencies and take all necessary precautions if out during the severe weather. If travelling I would advise that you plan your route and check local information, allow extra time, drive slowly and carefully and stay safe,” Mr Ross said.
Further information on how to prepare for severe weather is available at winterready.ie
The Department of Transport also publishes transport information for severe weather at dttas.ie/corporate/english/emergency-planning
As of January 2nd, salt usage to date this winter amounted to 38,400 tonnes, with stocks of 203,500 tonnes remaining.
The department said this compared to 96,000 tonnes of salt used over the winter of 2015/16 and some 130,000 tonnes used during the very severe winter of 2010/2011.
Transport Infrastructure Ireland provides details of motorway and national road conditions on tii.ie and tiitraffic.ie
Local authorities will also publicise local roads closures, and a number of local authorities provide mobile alert services which include updates on any such closures, Mr Ross said.
Information on traffic and road closures can also be found on the AA Roadwatch website, theaa.ie/roadwatch, and on local radio stations.
The Road Safety Authority provides information and safety advice for drivers, motorcyclists, cyclists and pedestrians at rsa.ie.
Central and east-southeastern Europe have in recent days been gripped by a mid-winter deep freeze and snowstorms.
With temperatures dropping below -30 Celsius, at least 25 people died over the weekend, mainly in Poland.