Temperatures of -6 degrees Celsius are expected in quite widely across Munster and south Leinster tonight, prompting Met Eireann to issue a low temperature warning.
All of Munster is included in the warning, along with counties Carlow, Kildare, Kilkenny, Laois, Wexford, Wicklow and Offaly.
Minimum air temperatures of -3 or -4 degrees are expected in the affected areas tonight, but locally these temperatures could drop to -5 or -6 in rural areas.
The warning is valid from 8pm tonight until 9am tomorrow morning, November 30.
Met Eireann has forecast for it to be very cold tonight nationwide, with frost forming widely, as cloud breaks develop and persist, leading to some icy patches.
The frost is forecast to be especially severe over Munster and Leinster.
A mix of cloud and sunshine is forecast generally, with the best of the sunny spells over the southern half of the country.
Top temperatures tomorrow look set to range to between just 4 to 6, where fog is slow to clear, to between 7 and 10 degrees elsewhere.
Met Eireann has said it will be cold overnight on Wednesday night with frost and fog returning especially to midland and southern areas, although it is expected to remain cloudier in the north where temperatures will hover around freezing.
With high pressure (anticyclonic conditions) forecast to dominate out to and including the weekend, there will be little or no change in the over all weather conditions for Ireland.
There will be no appreciable precipitation through this week, occasionally there may be some patchy drizzle on the coasts by the weekend, Met Eireann has said.
With the centre of the anticyclone directly over Ireland, winds over land will be light variable or calm throughout the outlook period.
Meanwhile, temperatures at night are forecast to be near to or just below freezing for the most part, but with fog likely to form each night there will be a limit to how low the temperatures will fall.
Typically each night temperatures will are expected to range between freezing and -3 degrees.