Winter is on its way back, forecasters have warned.
Temperatures are expected to plunge from the unseasonably mild highs of 13C in recent weeks to as low as minus 3C in the coming days.
The dramatic change in weather has prompted road safety chiefs to issue alerts to motorists about the dangers of frost, ice and fog for the rest of the week.
Met Eireann forecaster Pat Clarke said the shift signalled a return to normal conditions for this time of year, rather than any unusual switch in the climate.
"It's normal winter weather, but it's just a big change from what we had," he said.
Mr Clarke said daytime temperatures between 10C and 13C over the past few weeks - with night-time temperatures between 7C and 10C - were "very, very unusual" for late December and early January.
The mild conditions were a result of southerly winds bringing in rain and cloud.
"The last couple of weeks of mild weather might have fooled people to some extent," he said.
"But we are going to get a change now back to the cold."
While frost, ice and fog is expected, there is no imminent signs of any snow. Mr Clarke said it was too early to say if Ireland would escape widespread snow altogether this winter.