Wild weather: Winds brought down trees at Hornsby Heights.

Wild weather: Winds brought down trees at Hornsby Heights.

Nearly 21,000 homes in NSW were left without power and commuters faced delays after wind gusts of up to 110km/h brought down trees and power lines on Tuesday.

In Sydney, winds peaked at 82km/h on the harbour in mid-afternoon while the Illawarra recorded wind gusts of more than 100km/h.

Ausgrid reported power outages in 1,900 homes in Bundeena and Cronulla and Endeavour Energy said 19,000 of its customers were also left in the dark. Endeavour had opened three storm centres to manage the power outages.

SES volunteers retrieve a trampoline from the roof of a house.

SES volunteers retrieve a trampoline from the roof of a house. Photo: SES

The State Emergency Service said it was inundated with calls for help when people arrived home from work. It had received 670 calls across the state by 5.30pm and said its teams expected to work throughout the evening.

The combination of the season's strongest cold front and an intense low-pressure system delivered about half a metre of snow to Perisher and Thredbo ski resorts by Tuesday morning, with more falls since, said Rob Sharpe, a meteorologist for Weatherzone.

It is a bumper snowfall with some mountain areas likely to collect as much as one metre by the middle of next week.

Dangerous winds leave State Emergency Service inundated with phone calls: A tree crushes a roof in Hornsby Heights.

Dangerous winds leave State Emergency Service inundated with phone calls: A tree crushes a roof in Hornsby Heights.

"People will be celebrating," said Mr Sharpe, who added that powdered snow in some areas could be "an almost unheard of" metre deep once a second front moves through over the weekend.

The snow flurries will bring relief to the ski industry after a slow start. Thredbo was mostly green grass last week, with little snow at most other resorts.

The powerful weather system buffeted Sydney on Tuesday although the basin was spared the worst of the gale-force winds that had been tipped.

More wild weather should return on Wednesday, with the Bureau of Meteorology predicting "strong to gale force westerly" winds late morning.

Wind speeds should reach 40-60 km/h before easing to 20-30 km/h by the evening.

Temperatures should creep up again after Tuesday's top of just 16.7 degrees, with days of 19-21 degrees until Saturday.

The next front will bring cooler south-westerly winds, dragging Monday's maximum for Sydney back to 16 degrees to end June on a chilly note.

Even with the cold burst, Sydney should still end the month with maximums about 2.5 degrees above the long-term average.

With little rain expected, gauges are likely to record close to the current total of 68 millimetres, about half the typical June rainfall.