Temperatures dropped to as low as minus 4 degrees last night, but lows of minus 6 are predicted later tonight.
The yellow alert began at 9pm on Saturday and is expected to continue until 10am tomorrow morning.
The icy conditions this morning led to some minor accidents.
The condition of minor roads in the Rosses area were described as "dangerous" this morning.
And motorists are advised to drive with particular care on the Glen road between Loughanure and Annagry that branches off the main N56 tonight and tomorrow morning.
Motorists travelling to Loughanure from Annagry are also advised that the crossroads junction in Loughanure was extremely slippy this morning, with a number of cars sliding on the the main N56.
An articulated lorry went off the road at Crónasealg just outside Dungloe this morning, while cars were reported off at lower Loughanure and in the wider Dungloe area.
The driver of the artic lorry was treated at the scene in the early hours for shock and minor injuries.