A weather warning is in force in Northern Ireland until 06:00 GMT on Friday.
Some disruption is possible with rain, sleet, and snow forecast.
Accumulating snow is expected to be mainly over higher ground, while at lower levels many places will see little if any snow.
Above 150m, including the Glenshane Pass and Antrim Hills, 5-10cm (2-4in) of snow is likely to fall with a chance of 15cm falling in a few places.
There is an accompanying risk of icy conditions.
Police said the Shanes Hill Road area in Kilwaughter, near Larne, is impassable due to hazardous driving conditions as a result of snow and a collision in the area.
The Moyad Road in Kilkeel, County Down is also impassable and police have advised drivers to avoid the road between Spelga and Hilltown.
They urged people to drive with extra caution.
Irish weather service Met Éireann is warning of snow and ice across much of the Republic of Ireland.
A yellow warning for rain is also in place for several counties.
'Chance of power cuts'
The snowfall is anticipated to taper off later on Thursday, which could be followed by rain and drizzle, particularly in southern and eastern areas.
Towards the coast, it will probably be mostly rain and sleet, with snow inland spreading into the south during Thursday morning and towards the north for the afternoon.
Mini-blizzard conditions could develop with brisk easterly wind as well.
According to the Met Office, there is a small chance of power cuts, which could affect services such as mobile phone coverage.
There is also a slight chance that some rural communities may be cut off.
Roads could be impacted, which could cause travel delays and cancellations on some rail and air routes.
Northern Ireland saw its first big freeze of the year last month, as a cold Arctic blast brought snow and ice.
In the Republic of Ireland a snow and ice warning is in effect from 03:00 until 13:00 on Thursday for counties Clare, Tipperary, Galway, Laois, Offaly, Westmeath and Wicklow.
Counties Cavan, Donegal, Monaghan, Leitrim, Mayo, Roscommon, Sligo and Longford are under the same warning between 05:00 to 20:00.
A yellow rain warning is in place for Carlow, Dublin, Kildare, Louth, Meath, Wexford and Wicklow from 05:00 on Thursday until 05:00 on Friday.