Met Eireann is predicting a cold start to 2020 with frost and icy patches possible in parts of the country.
However conditions are expected to improve in the coming days, with highs of up to 11 degrees possible by Thursday.
A forecaster said: "A cold start to the new year with some frost and icy patches away from the West coast. Misty in parts too with some fog pockets.
"A dry day will follow with varying amounts of cloud. It'll become breezy with maximum afternoon temperatures ranging from 6 to 10 degrees, coldest over Ulster.
"Freshening southerly winds will become very blustery later along Atlantic coasts.
"Windy tonight and dry for the most part but increasing cloud will bring rain to the West coast by morning. Minimum temperatures of 5 to 8 degrees.
"Tomorrow, rain will spread from the west to all areas during the morning. It will turn drier for a time before more rain returns in the afternoon or evening.
"A mild day with maximum temperatures of 9 to 11 degrees. South to southwest winds will remain strong and very blustery throughout the day, before easing and veering Northwest in the evening."
And the warm weather is set to continue for the rest of the week, as a spell of high pressure moves in this weekend.
A forecaster added: "Mostly dry on Friday with a good deal of bright weather, especially in the east.
"Showers may affect northern parts of Ulster, spreading a little further south on Friday night. Maximum temperatures 6 to 10 degrees, mildest in the southeast. Winds light to moderate westerly, but strong and blustery along the north coast.
"Mostly dry with some bright spells as high pressure lying to the South of Ireland dominates our weather.
"Weak weather fronts close by may bring a little drizzly rain occasionally to parts especially in the North and West.
"The best of any sunshine will be in the south and east. Temperatures around average for this time of year with daily maximums around 8 to 10 degrees.
"Winds light to moderate southwesterly, a little fresher near north and west coasts. Becoming more breezy generally later in the weekend."
