Met Eireann has issued a warning for snowfalls of up to 3cm overnight on Saturday into Sunday as air temperatures are forecast to fall as low as -4 degrees.
The yellow level snow warning is for Ulster and Connacht but the forecasters say other areas may get a "lighter dusting".
Frost and ice will be widespread with warnings to watch conditions on untreated roads and footpaths tomorrow morning. The low temperatures of -1 to -4 derees are for all areas except Atlantic coasts.
The cold snap is set to last until Wednesday with severe night frosts and wintry showers of hail, sleet and snow expected.
Drivers were being asked to exercise caution on Saturday morning with road temperatures below zero on a number of routes. This followed subzero temperatures on overnight on Friday into Saturday and a snow and ice warning.
There were icy conditions throughout the Kells, Navan and Slane areas and around Ardee and Drogheda in Co Louth.
Black ice was reported on a number of routes in Sligo and Roscommon towns and there are treacherous conditions around Thurles, especially on the Nenagh/ Thurles Road (R498). In Castlebar, black ice is a problem particularly on secondary routes.
Gardaí in Ennis advised care on all routes on Saturday morning due to icy conditions; with particular care needed on the N85 Ennis/ Lahinch Road.
There will be more hail and sleet on Sunday with the top temperatures reaching between 3 to 7 degrees with a risk of freezing fog
Meteorologist Joanna Donnelly said Ulster, particularly in parts of Donegal, were likely to get a build-up of snow over the weekend.
“Elsewhere, it will be mostly passing wintry showers. The west should have more showers but some places will have absolutely none,” she said.
She said although there was a risk temperatures would drop to minus 7 degrees, most areas would reach between minus 1-3 degrees.
Ms Donnelly said weather warnings are issued on day-to-day basis and it was likely to stay “very cold” for the next week.
Forecasters have said it looked like it will become less cold and unsettled towards the end of next week.