Parts of Co Armagh are now under an amber weather warning for snow later this afternoon (Thursday).
The Met Office has issued the weather warning for the east of Northern Ireland, with Newry, Tandragee, Banbridge and Lurgan corridor largely affected. It is best to avoid travelling along the A1.
The warning comes into affect from 3pm and will last until 4am on Friday morning.
A yellow weather warning for snow and ice for the rest of the county will remain in place throughout the day.
As a result, travel delays on roads are likely with the possibility of stranding some vehicles and passengers.
Some delays and cancellations to bus, rail and air travel are also likely with some rural communities cut off from the main roads network.
The PSNI has advised motorists to take extra care on the roads, especially on those which may not have been gritted.
“Clear your windscreen of ice and snow before you set off and remember to slow down and increase the distance between you and the car ahead,” a spokeswoman said.
“Stopping distances increase greatly when weather conditions are poor, so slow down and leave a bigger gap between your vehicle and the vehicle in front, and drive as smoothly as possible.”
The Department for Infrastructure urged drivers to take caution this week as road gritting services would be disrupted by industrial action in a dispute over pay.
It said it would “prioritise the areas at greatest risk, such as high ground, and have targeted the available resources to deliver an overnight gritting programme”.