Temperatures will plummet below freezing tonight as a cold stretch of weather arrives.
Heavy fog will make driving conditions difficult in the west this evening, while 'wintry' snow showers are expected to hit on Monday and Tuesday.
And it will remain much colder for this time of year for the rest of the week, with Met Eireann saying that heavy frost can be expected.
Meanwhile, a status yellow fog warning is in place for Connacht, Cavan, Monaghan and Longford from 4pm until 10pm on Sunday.
A spokesman for the national forecaster said: "Mist and fog will clear this morning for a mostly dry day and bright to begin. It will be coolest and cloudiest across the northern half of the country with the best of sunshine in the south.
"Outbreaks of light rain and drizzle will move into western and northern counties by evening. Highest temperatures of 9C to 14C, mildest in the south. Becoming breezier with a moderate northwest breeze picking up through the day.
"Cloudy to begin tonight with scattered outbreaks of light rain moving southwards overnight, followed by much colder air.
"Scattered showers of sleet or snow will move over Ulster later in the night with clearer weather developing. Northerly winds will be moderate to fresh, strong at times on Ulster coasts.
"Lowest temperatures of -1C to 3C, coldest in Ulster with frost forming locally.
"Tomorrow will feel cold and be breezy. It will be driest and brightest across the south and east. Light scattered showers of rain or sleet, possibly snow on high ground, will mainly affect Ulster and north Connacht.
"Showers will be more isolated elsewhere with sunny spells. Highest temperatures of 4C to 8C with added wind chill from a fresh northerly wind."
Monday night will stay cold with wintry snow showers as temperatures fall again to a bitter -3C. The freezing conditions will lead to icy stretches on many roads nationwide.
Tuesday will be breezy with scattered showers and bright spells, but will also see wintry conditions and longer spells of rain in the afternoon.
Temperatures will again fall to -3C, with a further risk of snowy spells overnight.
It will be less cold on Wednesday as things heat up a touch, but sadly, early indications suggest it will be very wet.
