It's set to be a drier than average winter for the Illawarra and eastern Australia with the Bureau of Meteorology predicting it unlikely for winter to bring heavy rainfalls.

BOM's manager of long-range forecasting Andrew Watkins said the next three months were looking to be drier than average with warmer than average days.

He said models were currently showing June rainfall for NSW likely to be below average.

"Drier than average conditions typically mean more cloud-free nights, which increases the risk of frost in susceptible areas," Dr Watkins said.

But it doesn't mean we'll see no rain at all.

"It is the southern wet season after all - but it does support the model outlook for a drier than average winter, with the possibility of more evaporation than normal," Dr Watkins said.

The outlook for Illawarra ski bunnies is so far not faring well either.

"It's great to see some snow early on, but unfortunately early snow doesn't ... relate very well to the snow season in general.

"We're seeing some patterns that might bring warmer and drier conditions and unfortunately that tends to mean we'll have a shorter season. Possibly an earlier end to the season with a bit shallower snow depths."

Meantime, preliminary figures show this autumn is likely to go down in the record books as one of Australia's five warmest. For NSW, the ranking for the March to May period is also likely among the top five warmest.

This even accounts for the wintry blast to the end of the season which prompted Perisher to open their season a week early on Friday, after multiple blizzard-like days bringing a total of 75cm of early snowfall.

It comes as areas in the Sydney Water catchment - including the Illawarra - will go on level one water restrictions from Saturday. Dam levels have plunged by about half in the past two years to be about 53 per cent full as of Thursday - the lowest inflows since the 1940s.

There will be a three-month grace period before fines of $220 for individuals and $550 for businesses are imposed.

Standard sprinklers or water systems are banned, though residents can water their gardens with a watering can or bucket. Lawns can be watered by hand held hose before 10am or after 4pm, as long as the hose is fitted with a trigger nozzle.

Residents can wash vehicles and buildings with a bucket, a hose fitted with a trigger nozzle or high pressure cleaning equipment and can top up an existing pool or spa to replace water that has been lost through evaporation.

Cleaning hard surfaces like paths, driveways and paved areas with a hose is also banned.

Exemptions include using recycled, grey, rain, bore and river water as well as water parks, firefighting, dust suppression, concrete mixing and automatic car washes.