Met Eireann's Status Orange weather warning for "dense" fog remains in place for most of the country this morning with further cold conditions expected tonight.
The alert is in effect until 8am this today for Dublin, Carlow, Kildare, Kilkenny, Laois, Wexford, Wicklow, Offaly, Westmeath, Meath, Galway, Mayo, Roscommon, Clare, Cork, Limerick, Tipperary and Waterford.
The warning reads: "Mist will thicken into fog overnight and will be dense at times."
On driving in the foggy conditions, AA Roadwatch said: "Keep in mind that fog can make tail lights seem further away than they really are, so slow down and keep further back from the vehicle in front.
"Use your fog lights, but remember to turn them off when you no longer need them."
Irish weather forecast: Met Eireann issues Status Orange fog warning for 18 counties
Conditions are expected to remain relatively mild today as temperatures reach highs of up to 15C, however it will be a bitterly cold night with the possibility of frost and further fog in places.
A forecaster said: "Cloudy and misty in many areas this morning, with patches of drizzle and fog.
"Clearer, mainly dry conditions in the north and northwest will extend slowly southwards as the day progresses, with sunny spells developing.
"However, it will remain cloudy and misty in most parts of Munster and south Leinster, with rain and drizzle becoming persistent in parts of the southeast during the morning and in Munster during the day, with a few heavier bursts developing.
"Maximum temperatures 10 to 15C, coolest in the east, in light to moderate easterly breezes.
Irish weather forecast: Temperatures to hit 15C today but cold frosty nights ahead this week
"Tonight will be mainly dry, with any patchy drizzle in the southwest largely dying out.
"Most areas will have good clear intervals, but it will be cloudy in many parts of Munster.
"As winds slacken, a few patches of mist and fog will develop.
"Lowest temperatures 0 to 4C, with frost in many areas, but milder in the southwest under mostly cloudy skies."
Further mist and fog is possible on Wednesday night with lows of just 2C, while on Thursday temperatures are expected to plummet to freezing overnight.
