Sydney, Brisbane and Canberra, you're going to get drenched this weekend. So will a huge area of eastern New South Wales, Queensland and Victoria.
Damaging winds, extremely heavy surf and abnormally high tides (exacerbated by the strong winds and high seas) are also highly likely.
Bottom line: not a good weekend to have Paddle Pop stick races in stormwater drains.
As many as 26 major river valleys in eastern New South Wales are tipped to experience flooding. You can read the full list here. There are also flood warnings for Queensland and a marine wind warning for the Eastern Gippsland region of Victoria.
Here are the bits of New South Wales likely to cop the worst of the weather:
And the Queensland map:
So what's causing it?
Well, the first thing you should know is that this is a decidedly unwintry weather pattern. It's a lot more like the weather pattern you see in a wet summer where moist, rain-laden air from the Coral Sea is dragged southwards.
Here's the forecast weather map for Saturday morning. Can't read a weather map? All you need to know is that air rotates anti-clockwise around a high pressure system (the big H). So as you can see, air from the Pacific around New Caledonia is making a beeline for the New South Wales and Queensland coast.
Throw in the low pressure that's formed over the inland (long story short, lows mean rain) and you've basically got an enormous DIY rain-making kit parked over about a quarter of Australia.
It's worth noting that when the Bureau forecasts flooding, it gets it right in 70 percent of cases. So while forecasts of flooding are of great concern, this weather system will still be welcomed by farmers in large parts of central New South Wales, northern New South Wales, south-east Queensland and eastern Victoria -- where rainfall has been well below average in recent months.
Overall, the Bureau says that weekend rainfall totals of 80 to 150 mm are likely for much of the area with localised falls between 200 to 300 mm.
The rain is set to continue into Monday and Tuesday. At that point, something interesting could happen. This is a weather event involving tropical air. Yes, that happens sometimes, even in the first month of winter.
But a cold pool of upper atmospheric air is forecast to cross the south-east on Monday. This is not the broad swathe of cold air you get with your typical southern Ocean cold front, but an isolated pocket which could cause a rapid drop in temperatures in a relatively small area.
If, for example, the cold pool tracks over the middle third of New South Wales, then snow could fall in the Blue Mountains or the New South Wales northern tablelands, while the Snowy Mountains further south see only rain.
That's only a maybe for now. Hard to tell where it'll end up. The path of cold pools is notoriously difficult to predict.
We'll keep you (Huff)posted on that one. For now, go dig your umbrellas and raincoats out of the closet if you live on the east coast. And stay safe.