WINTER has come five months early with a cold snap bringing a light dusting of snow to some parts of NSW.

Southern NSW, Victoria, Tasmania and South Australia have been hit by an unseasonal cold front, with temperatures plummeting to near zero in the Snowy Mountains.

Thredbo and Cooma have reported a brief flurry of snow.

Bureau of Meteorology duty forecaster Jane Golding said the cold front had brought a lot of cold and dry air with it and also thunderstorms, apparently from well south in the Southern Ocean.

She said there has never been summer snow in Cooma since records began there in 1973.

Meanwhile, more than 1000 Perth households have been left without power, as power consumption peaked to an all time high as Perth sizzles its way through a heatwave.

Power consumption peaked to 3790 megawatts on the south west electricity network in WA today rose to 41.7C, surpassing the previous peak level of consumption set in February last year, Western Power said.

Western Power system management general manager Ken Brown said power consumption was expected to climb to 4000MW or more later on Monday.

"The increase in the number of air-conditioners, pool pumps and flat screen televisions in particular is the main cause of the increase in power consumption," Mr Brown said.

About 1300 households were without power, caused by heat-related outages, by early on Monday across the Perth metropolitan area.

Western Power said it was installing generators in locations where demand for power has jumped since last year.

Temperatures soared to 42.9C yesterday and had surpassed a forecasted 41C today to hit 42.2C.

The Bureau of Meteorology has forecast a top of 37C tomorrow before the mercury dips to 30C on Wednesday.