A STATUS Yellow warning has been put in place for tomorrow and Saturday with heavy rainfall of up to 50mm expected to hit the country.
They added: "Fog patches are likely to form during the early part of Wednesday evening, becoming more widespread overnight with the visibility falling below 100m in places".
Weather conditions today and through tonight will be ideal for the formation of thick and troublesome "radiation fog", experts say.
Up to four inches could fall over those two days, with forecasters warning of blizzards and frequent lightning strikes, which could cause power cuts and mass travel disruption. Some bright or sunny spells are expected where fog has cleared and especially in coastal counties.
Still remaining rather cold with highs of 6C.
Friday is set to be breezy followed by heavy rain in Munster or Connacht. Afternoon temperatures will range from 5 to 9 degrees Celsius, coldest in the north. Winds will be strong to gale force and gusty southeasterly.
It will be windy and mostly cloudy elsewhere too with the rain spreading eastwards; some heavy rain is expected by dawn. Overnight fog and any frost should clear.
Britain is wrapping up for another chilly night with temperatures expected to drop to freezing widely with lows of -2C (28.4F) or -3C (26.6F) in rural regions.
"Top afternoon temperatures 3 to 7C".