The east coast of NSW is in for a day of wild weather, with heavy snowfall in some areas causing significant delays on major roads.

Both directions of the Hume Highway south of Sydney between Goulburn and Sutton Forest are affected by snow, and motorists have been advised to avoid the area.

The Transport Management Centre said a number of trucks had lost traction on the slippery highway and were blocking lanes.

Drivers said they have been at a standstill for more than an hour, describing the traffic as "horrendous".

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Truck driver Vince told ABC local radio he had never seen as much snow in the area before.

"[It's] beautiful. The drive is sensational going south. I haven't seen anything like it," he said.

"It's just white, white, white. I'm loving it."

Parts of the upper Blue Mountains have also turned white, with residents in Blackheath and Medlow Bath waking up to surprise spring snow.

Drivers are warned to take care when travelling on the Great Western Highway between Leura and Bathurst due to icy conditions.

Goulburn has been blanketed by snow in a surprise Spring fall. ( Supplied )

In Sydney, 20 millimetres of rain is expected, and the Hunter Region can expect 50 millimetres, with rain expected to stick around for at least the next 24 hours.

But frustratingly, the Bureau of Meteorology (BOM) said storms forecast for northern NSW would increase the fire risk for crews who continued to battle blazes near Tenterfield, Armidale and Glen Innes.

"Obviously if we've got storms they can bring erratic wind conditions, so you may see lightning strikes result in more fires, and that could be a difficulty for firefighters who are already stretched thin in the north," forecaster Jordan Notara said.

"We will see those winds strengthen to around 40 kilometres per hour."

Blackheath residents say they weren't expecting any more snow this year. ( Twitter: Donna Coventry )

The weather system will bring significant rainfall to southern and central parts of the state and the BOM has warned of flooding along the Myall River, Paterson and Williams Rivers and Tuggerah Lake.

But those in the west facing a devastating water crisis, with supplies fast drying up, will miss out again.

The trough and associated cold front was due to move off the coast later on Tuesday, but another cold front is set to arrive on the weekend.