We should all be grateful that the 2021 AFL Grand Final between the Melbourne Demons and Western Bulldogs is being played at Optus Stadium in Perth rather than at the MCG, because Melbourne's Saturday weather does not look good.

Sydney isn't likely to have its greatest weekend of spring weather in history either, although Melbourne will definitely be a lot worse on Saturday at least (if cold, showery weather is not your thing), due to cold, unstable air in the wake of the strong front passing through Tasmania and southern Victoria on Friday afternoon.

In Melbourne:

• Saturday is tipped to reach just 13°C as cold southwesterly winds sweep across the city, bringing with them the odd shower. It's not going to be super wet, but that wind will have a serious bite to it.
• On Sunday there will still be a definite chill in the air, with tops around 15°C, but the wind is likely to die down so it shouldn't feel too bad outdoors.
• Both days will peak will below the September average max of 17.3°C.

Image: That tongue of frigid polar air can be seen licking Melbourne this weekend. Source: ECMWF model. 

As for Sydney:

• Saturday looks pleasant enough in Sydney, if a touch breezy throughout the day, with southwesterly winds swinging round to the south and southeast late in the day. A top of 21°C is expected but it may feel a little cooler with that wind.
• Those southerlies and southeasterlies will keep things even cooler on Sunday, restricting Sydney to a top of just 18°C. A shower or two is possible, most likely in the morning.
• Sydney's average September max is 20.1°C, so this weekend will definitely be on the coolish side later in the weeekend, especially for the last week of the month.

So overall, Australia's two most populous cities won't be too wet, but conditions outside won't be too enticing either. As for the other capitals:

Perth, all importantly, will be absolutely bonza for the footy, with fine conditions and a top of 27°C on the cards for the first ever AFL Grand Final in the west (it was moved there due to the Covid situation in Victoria). We told you earlier this week that a cool, wet change is due in Perth on Sunday, and that it wasn't likely to arrive early and spoil the grand final party. We can say that with greater confidence now.

Adelaide will remain cool in the wake of the front that crossed southeast Australia on Friday, but it should stay dry, if a little cloudy. Expect tops of 16°C and 19°C.

Darwin will be Darwin! Tops of 33°C and 34°C are likely, with just the slight chance of a light shower.

Canberra will be cool but mainly dry with tops of 16°C both days and old Jack Frost making an appearance on Sunday and Monday mornings.

Hobart is in for some seriously cold weather, with a top of just 10°C on Saturday and the chance of snow in the suburbs as the snow levels dips to just 100 or 200 metres. Sunday will be a little warmer with a max around 14°C.

Brisbane will be immune to all the cold stuff coming from down south on Saturday, with a top of 30°C. But by Sunday, the southeasterlies arrive and the temp will only reach 24°C or thereabouts with the chance of showers.