The forecaster says heavy thundery showers will increasingly turn wintry, especially over higher ground with some accumulations likely over hills.
The warning is valid until 10am tomorrow.
It comes after heavy hail storms overnight which have continued this morning and into the afternoon.
Strong winds are also making driving conditions very difficult.
Gardai say their officers are on patrol – and Donegal County Council grifters lorries will be in action this evening and overnight.
It is bitterly cold across the North West with accuweather saying the real-feel temperatures are of -4C.