The national forecaster had earlier issued a low temperature and ice warning for Leinster, Cavan, Monaghan, Munster, and Connacht, which has since expired and a new alert has been issued for the entire country from 6pm this evening.
“Very cold this evening, tonight and on Wednesday morning with severe frost and icy stretches,” the warning stresses.
The sub-zero temperatures will lead to difficult travelling conditions as well as issues for vulnerable people and animal welfare issues.
This warning will be in place until 11am tomorrow.
For those planning to travel to the north today, the Met Office has issued a Yellow Snow and Ice warning for every country in Northern Ireland.
This comes into effect from 5pm this evening until 23.59pm on Wednesday, which will then continue for another 24 hours, except for Armagh.
The Met Office UK has said for these counties: “Ice will readily form on untreated surfaces this evening leading to hazardous conditions.”
There is also a weather advisory of Arctic air bringing winter hazards this week, which is valid until 12pm on Friday.
Sharp to severe frosts are expected with icy stretches on roads and pavements this week, Met Éireann said.
Some sleet and snow will occur, mostly in the northern parts and on the hills.
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The lowest overnight temperature of -6.3C was recorded at Moore Park, Co Cork at 5am, Met Éireann said.
Frost and ice will gradually clear in most parts of the country this morning, however it might linger all day in the south of the country.
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Ulster will see rain, sleet and snow today, as north Connacht and north Leinster can expect rain and drizzle by mid-morning. However, further south will enjoy the brighter conditions and sunny spells.
Temperatures will range between 3 and 7C, with light to moderate winds.
Tonight will bring a mix of clear spells and patchy clouds with scattered outbreaks of light rain, drizzle, sleet and snow for a time overnight.
The western and northern parts of the country will see wintry showers overnight.
Temperatures will drop to –4 to –1C tonight, with sharp to severe frost and icy stretches forming and a light and variable breeze leading to patches of freezing fog to develop.
Cold Arctic air will bring widespread frost and ice, leading to hazardous travelling conditions until Friday.
The north and northwest will see the most frequent wintry showers.
The lowest overnight temperatures this week are forecast on Wednesday night, with temperatures dropping to –5 to –1C, and on Thursday night, with –5 to –2C.