Ireland will enjoy highs of possibly 16C on Thursday but temperatures will plunge to as low as -2C over the weekend.
Met Eireann is predicting a warm and mostly dry spring day, with sunny spells expected at times.
However, the north and west will experience cooler temperatures with light rain, as the south is set for the best conditions.
A forecaster said: "Patchy rain and drizzle across parts of Ulster and Connacht today.
"However, much like recent days it will be milder and brighter elsewhere with spells of spring sunshine developing, after a damp and misty start with fog in parts.
"Some sunshine breaking through too across the north and east later. Highest temperatures ranging 9 to 15 or 16 degrees, in light to moderate northerly winds."
Temperatures will drop to as low as 1C overnight in places such as Cork, despite afternoon highs of 15C being forecast.
The weather chiefs are predicting frost for some areas on what will be a mainly dry and calm night.
The forecaster said: "Cold, dry and calm tonight with clear spells.
"Lowest temperatures of 1 to 5 degrees. Some frost setting in, along with mist and fog patches."
It's only going to get colder this weekend, with daytime highs of just 10C being predicted for Saturday.
And Saturday night will be bitterly cold as temperatures are set to plummet to -2C in parts of the country.
"Overall Saturday will be dry with a mix of cloud and sunny spells (brightest skies likely later in the day).
"However, moderate northeast breezes will feed in a few light passing showers to eastern counties.
"Highest temperatures 7 to 10 degrees, coolest for northern and eastern coasts owing to onshore winds here.
"After-dark turning cold with long clear spells and widespread frost; overnight lows of -2 to +1 degrees, in light to moderate northeast breezes."
