The likelihood of snow falling over the ranges all the way up into Queensland also has emergency services warning motorists and those planning outdoor activities such as skiing or camping to "plan carefully for the cold conditions".

Blair Trewin, senior climatologist with the bureau, said the last time Australia had such a large northward spread of snowfall was in May 2000.

"On the current forecasts, [the coming cold outbreak] won't be quite as significant but it may be in a broadscale sense," Dr Trewin said.

The front will send the mercury dropping in Adelaide and Melbourne on Saturday, while Sydneysiders will experience the sharp sting of winter on Sunday.

The Harbour City is expecting a mild, sunny day on Saturday with a top of 19 degrees before showers and wind help limit Sunday's expected top to fifteen degrees, according to updated forecasts.

Inland areas such as Penrith and Richmond can expect a top of 13 degrees on Sunday, while Katoomba will get a maximum of just 6 degrees with snow possible on both Sunday and Monday, the bureau said. (See Sunday's synoptic chart below.)

A low will then form over the Tasman, directing winds and more showers towards Sydney for a day or two after that, Rob Sharpe, a meteorologist with Weatherzone, said.

A second front moving through on Wednesday will make the city feel very much like the middle of winter.

"It will prolong the cold spell until the middle of next week," Mr Sharpe said.

Snow dump

Proof of the big chill will be the extent of regions across Tasmania, Victoria and NSW experiencing zero temperatures, the Bureau of Meteorology said.

A belt of low pressure systems is a fairly permanent feature of Antarctica. One of those lows - at a latitude of about 55-60 south - is currently to the south of Tasmania and further from the Antarctic coast than usual, Dr Trewin said.

The last time "meaningful snow" fell in Canberra was during the May 2000 event, and the coming cold jolt is "one of the better shots" for the capital to get another dusting even if the chance is only about 20-30 per cent, he said.

Conditions, though, will feel much chillier after a run of relatively calm, if cool, days.

"We're expecting temperatures will plummet, winds will be fresh to strong, and snow will fall down to low elevations," Barry Hanstrum, NSW regional director at the bureau, said.

Areas likely to receive snow include Orange and Bathhurst in NSW and the tops of mountains in south-eastern Queensland. (The bureau's chart below shows where snow is likely by 10am AEST on Sunday.)

Mr Sharpe said the main alpine ski resorts were going to fare well out of this weekend's dump and follow-up falls.

By the middle of next week, some resorts will get well over 50 centimetres of snow - too late, though, for most schoolchildren in NSW and Victoria whose holidays expire this weekend.

"Particularly if it stays cool, [the main resorts] will do well for the next few weeks," Mr Sharpe said.

However, the cold snap may catch some people ill-prepared.

NSW SES Commissioner Adam Dent said people should take extra care if snow is forecast in their area, with power outages also possible.

"Heavy snow can quickly make roads slippery and impassable, so if snow is forecast delay non-essential travel," Mr Dent said in a statement.

"Snow can bring down trees and branches, blocking roads and damaging property, so take the opportunity ahead of forecast snow to trim overhanging trees and branches and, if isolation is likely, stock up on food, fuel, medicine and other essential items," he said.

Weatherzone is owned by Fairfax Media, publisher of this website.