The warning was issued in the early hours of Thursday morning, at 2am, and will remain in effect until 10am, with widespread fog forecast throughout Ireland.
"This results in a reduction of the air's ability to hold moisture which allows water vapour to condense into tiny water droplets eventually leading to the formation of fog".
"Fog will thin slowly later on Thursday morning, although some patches may persist into the afternoon in the west of the warning area". "The heat rises and then it cools down and that is why you get fog forming".
A MET Office weather warning for fog is still in place this morning with thick fog still expected in many parts of the county.
It will be cold tonight, with dense fog and some frost for a time especially in midland, northern and eastern areas with overnight lows of -1° to +3°.
Where is radiation fog in the United Kingdom?
BRCA mutations don't hurt breast cancer survival
BRCA mutations are among dozens of other genetic mutations that raise the risk of breast or ovarian cancer. The researchers found that 12 percent of patients had a pathogenic BRCA mutation.
A Met Office severe weather warning covers a portion of western Britain through tonight until 11am tomorrow.
Mr Wilson said: "There is a lot of radiation fog around at the moment".
It is most prominent in areas where skies were clearest overnight.
"The fog for most areas will lift later on and we will see some brightness in the west but in eastern parts it is going to stay quite cold today with some patches of rain". Lowest temperatures 4 to 8 C.