Saturday looks set to be the hottest day of the year so far - but temperatures will drastically plunge from Sunday.
Met Eireann is predicting that parts of Ireland are to bask in sunny skies with heat of up to 21 or 22C on Saturday.
However, the glorious weather will be short-lived as daytime highs won't beat 13C on Sunday, and temperatures are expected to plummet to as low as -1C that night.
A forecaster said: "Saturday will see some bright or sunny spells, but cloudy in many areas, especially in the north.
"Scattered showers also, most of them in the northern half of the country. Warm in most parts, with maximum temperatures of 18 to 21 or 22 Celsius, but cooler in the north and northwest, with maximum values of 14 to 17 degrees.
"Winds mostly light, northeast or variable. Mostly dry overnight, but some scattered showers or patches of rain will occur and it will gradually turn much colder from the north. Min. 3 to 6 Celsius, in moderate northeast winds."
They added: "Sunday will be cold and breezy, but mainly dry, with sunny spells developing. One or two isolated light showers are possible, especially in the northeast.
"Max. 8 to 13 Celsius, coldest in the north and east, in mostly moderate northeast winds, fresh to strong on exposed coasts.
"Dry overnight, but cold, with a touch of frost possible. Min. minus 1 to plus 2 Celsius."
The weather chiefs say Monday to Thursday will be much cooler, with highs of 13C to 15C being forecast.
Meanwhile, Ireland may see highs of 19C on Thursday but nearly all of the country will experience rainfall.
There will be some clear spells, but most areas will be cloudy with some heavy rain expected in parts of the midlands.
The forecaster said: "Mostly cloudy this morning, Thursday, with scattered outbreaks of showery rain. Mist and fog patches also, mainly in the southwest.
"Brightening up gradually, with sunny spells developing, but scattered showers will occur also, some of them heavy in the afternoon and early evening, especially in the north and northwest and later today in parts of the midlands.
"The southern half of the country will become mostly dry. Maximum temperatures 15 to 19 Celsius, but cooler on southern and western coasts with onshore breezes.
"Winds mostly light to moderate southerly, with some sea breezes developing."
Thursday night should be mostly dry and clear, despite a few showers in the west.
"Tonight will become mainly dry, with clear spells, but a few scattered showers may occur along Atlantic coasts. In calm conditions, some mist and fog patches will develop. Minimum temperatures 6 to 8 Celsius."
