Highest temperatures will be just between 1 and 5 degrees, and temperatures are set to drop tonight to between -5 and -2 degrees again.
The cold spell is due to break tomorrow night.
After another cold and bright start, temperatures will steadily rise on Friday and the weather will become milder, and often wet and windy, for the weekend.
A Status Yellow low temperature and ice warning for all of Ireland was extended for another day and will now be in place until noon today, Thursday.
Met Éireann has also extended a status yellow snow and ice warning for Donegal, Leitrim, Mayo and Sligo, which will be in effect until 11am today, Thursday.
A weather advisory for Ireland remains in place until midday on Friday as cold Arctic air brings difficult conditions this week.
Carlow Weather’s Alan O’Reilly has forecast the freezing temperatures to be followed quickly by mild weather and a potential “massive storm” on Sunday.
Speaking to RTÉ Radio One’s Claire Byrne yesterday morning, Mr O’Reilly said we were set for a “dramatic change”.
“We are set for a dramatic change for the weekend. If you don’t like the cold weather, it’s good news, but if you don’t like the rain then it’s not good news,” Mr O’Reilly said.
“We’re in for a massive storm on Sunday, very strong gusts and very heavy rain.”
Looking further ahead, Mr O’Reilly said the forecast is for unsettled weather next Monday and Tuesday.
“We’ve had an exceptionally mild winter so far. Most people are happy enough when it is cold and crisp and dry, and there’s a nice blue sky, but the cost of the heating is probably the biggest issue,” he said.
Mr O’Reilly added that Ireland was only halfway through winter, since meteorologists determine winter to be from December to February.
“The weather models show that we could have another high-pressure system at the start of February so we could see another cold spell yet. But the first half of the winter will certainly go down as mild,” he said.