People are being advised that cold weather over the next few days is going to be a "bit of a shock to the system".
Colder weather conditions are expected right across the country from this morning.
Met Éireann has issued a status yellow snow/ice warning for Donegal until midnight, where hail, sleet and snow showers are expected.
Meanwhile, a cold weather advisory is in effect for the rest of the country over the next two days, with people being told to expect "sharp to severe frosts and icy stretches".
Alan O'Reilly, forecaster with Carlow Weather, told Breakfast Briefing that the current forecasts suggest there'll be some very wintry weather over the next week.
He said: "There's really going to be a sudden drop in the temperature people feel outside this morning... and unfortunately also some heavy showers this morning. Some of those will be hail and sleet.
"It's going to stay cold now for the next couple of days - particularly today, tomorrow and into the weekend.
"The biggest issue - apart from maybe the hail showers this morning - will be the lower temperatures tonight. That will result in very icy conditions tomorrow morning."
Mr O'Reilly said a very strong north-west wind tomorrow means the wind-chill factor is going to make it "feel much cooler again tomorrow" - warning it's likely to prove something of a shock to the system for people.
He explained a Met Éireann advisory means conditions haven't reached the level of a warning, but people are still being advised to be aware of the weather.
While a warning is in place for Donegal, there's a nationwide risk of icy patches - particularly in parts of Leinster.
Mr O'Reilly said: "Tomorrow morning... is going to be the first winter morning where you're going to be scraping ice, and you're going to need to allow some extra time for your journey."
He added that a risk of lying snow and sleet showers is higher in parts of Northern Ireland, where the UK Met Office has issued a status yellow ice warning for Antrim, Fermanagh, Tyrone and Derry.
