Weather forecasters have issued an orange alert with snow and ice threatening northern counties and wintry weather set to last until at least Good Friday.
Met Eireann said Cavan, Monaghan and Donegal are facing the worst of the wintry conditions with a combination of strong winds and a mix of rain, sleet and snow at risk of causing blizzards and drifting.
It has also warned of localised floods in eastern counties and strong winds across the country.
Snow is expected to be about 3-4cm (1.2-1.6in) deep, with the Mournes and parts of Antrim also badly hit, but cities and lower lying areas will be relatively unscathed.
Evelyn Cusack, Met Eireann forecaster, said a mass of polar air would continue to influence the country's weather up until Good Friday. She said: "A band of rain is moving north where it will hit colder air, the polar front if you like, and that occurs at our latitude.
"Ireland will be the battleground for the next few days with rain moving to snow as it hits the colder air."
Temperature variations of up to 10C (50F) are expected on Friday morning with some parts of Munster up at about 11C (51.8F) and parts of northern counties as low as 1C (33.8F).
Frost is also expected to affect farming and spring planting over the next week.
"Temperatures are several degrees below average in parts of the country, but it's not exceptional for the time of year," Evelyn Cusack said.
Met Eireann has introduced new colour coded weather alerts, with orange issued to warn of conditions which have the capacity to impact significantly on people in the affected areas. The forecast is for heavy and persistent rain expected to sweep across Munster, Connacht and Leinster with spot flooding from this afternoon.