Temperatures could plummet to lows of -3 in Donegal overnight.
There will be clear spells with widespread sharp or severe frosts with icy patches in most areas.
Fog will develop and will become dense overnight in certain parts of the county.
It will be cold this afternoon with sunny spells and scattered wintry showers, mainly in the west.
Highest temperatures of 3 to 6 degrees with moderate to fresh and gusty northwest winds.