Met Eireann has forecast freezing conditions tonight but says temperatures will be mild during the week.
Today will be a "largely dry and bright day with long spells of sunshine" with highest temperatures of 6 to 9 degrees.
But tonight, temperatures will plummet to as low as -3 degrees.
The forecast says: "Dry and very cold with long clear spells. Lowest temperatures of -3 to +1 degrees, generally with a widespread frost setting in.
"Mist and fog will develop too in light breezes."
Dry conditions will remain on Monday.
The forecast says: "Monday morning will brighten up as any lingering fog and frost clears, leaving a generally dry day with good spells of sunshine, however it will become cloudier from the west during the afternoon.
"Highest temperatures of 4 to 6 degrees over the northern half of the country, a milder 7 to 9 degrees and east in light to moderate southeasterly winds, becoming fresh at times in the southwest during the afternoon."
Rain is expected on Monday night, with lowest temperatures of 0-5 degrees.
"Coldest early on over much of Ulster and Leinster with lowest temperatures there of 0 to 5 degrees. Milder and cloudier conditions in the west and southwest will extend eastwards across the country, with outbreaks of rain following, becoming widespread and heavy in places later in the night in moderate to fresh southerly winds."
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