Snow is falling on the Snowy Mountains, Sydneysiders are bracing for damaging winds and much of the state's east woke up to rain today.

It is hard to believe it's summer in NSW, let alone Christmas.

But that's just what happens, forecasters say, when you combine a cold front moving through western south east NSW and a low pressure system over the Tasman Sea.

"We had some cool overnight temperatures in Perisher, Falls Creek and Charlotte Pass, where we also saw some snow," Weatherzone meteorologist Micaela Weber said.

Ten millimetres of the white stuff fell over Charlotte Pass, where overnight minimum temperatures dropped five degrees below average to -1.

"It is kind of wet snow so it's not really nice dry snow," Ms Weber said.

"But it is possible when you have a cold front coming through and extremely cold temperatures."

Cabramurra also recorded a minimum temperature of -1, which is 10 degrees below average.

But any hopes of a white Christmas are premature as the cold front is expected to pass before Saturday.

"We could see more snow showers until Tuesday night but as soon as the cold front has passed a warming will occur and temperatures will go up again," Ms Weber said.

Sydney is heading for a mostly sunny Christmas Day, with a top of 26 degrees and the possibility of showers in the afternoon.

Meanwhile, the Bureau of Meteorology issued a severe weather warning this morning for the Snowy Mountains, Sydney, the Hunter, Illawarra regions, as well as the Southern and Central Tablelands.

Damaging winds averaging 50 km/h with peak gusts of up to 100 km/h are expected.

The SES has advised people to move vehicles under cover or away from trees, to secure loose items around homes and to keep clear of fallen power lines.

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