Met Éireann has issued a Status Yellow fog warning today (Wednesday, November 27) for all of Connacht and several other counties.
The other counties affected include: Cavan, Donegal, Monaghan, Dublin, Kildare, Laois, Longford, Louth, Meath, Offaly, Westmeath and Wicklow.
The warning will come into place from this evening at 4:00p.m until 6:00a.m tomorrow (Thursday, November 28).
The national forecaster has warned of patches of fog and freezing fog, which is expected to thicken this evening and tonight.
Lowest temperatures will range between -3° to 0°, but will be milder for Munster counties, with the arrival of the rain.
It will also become much breezier with moderate to fresh southeast winds developing. Southeast to south winds are expected to reach a gale force of six or higher tonight.
The UK Met Office has also warned of widespread frost developing across Northern Ireland, along with freezing fog tonight, which could become “extensive” with minimum temperatures of -3°.
Fog is expected to clear in Northern Ireland on Thursday morning, with outbreaks of rain and showers foretasted for the weekend.
Fog set to clear
The frost, mist and fog will clear on Thursday morning across the country and it will be dry in most areas with some sunshine, especially further to the north and east.
However, it will become mostly cloudy in the morning the south and west, with some rain and drizzle, mainly in the south-west.
Cloud will build elsewhere too through the day and it will become breezy, and while there will be some further scattered outbreaks of rain and drizzle in the south-west and south, it should hold mainly dry elsewhere.
The national forecaster has said that the highest temperatures in the north will be 5° to 12° with south-easterly winds increasing mostly fresh and gusty, stronger in some coastal parts.