If you think it was hard to pick the difference between a Shane Warne leg spinner and his famous flipper (the ball that kept low and straight instead of spinning), then wait till you see the weather forecast for the 2023 Boxing Day Test between Australia and Pakistan at the MCG.

Unsettled weather is heading Victoria's way, that much we can say with great confidence. But whether it directly affects Melbourne on December 26 remains to be seen.

It might rain heavily at the cricket and it might not. There might be storms and then again, there might not. If it sounds like we're calling both heads and tails at the toss, here’s the reason for the uncertainty.

Image: The weather forecast for Melbourne on Boxing Day is all a bit of a blur. Source: AAP Image/Scott Barbour.

• An upper-level cut-off low pressure system with an associated pool of cold air is going to cross Victoria on Christmas Day and Boxing Day. That's one part of the recipe for instability – as in rain and storms.
• The low will also interact with warm, moisture-laden air that has travelled over Victoria from the Tasman Sea. That airborne moisture is another other key ingredient for meteorological mayhem.
• What really matters now for day one of the Boxing Day Test – and to a lesser extent day two – is the positioning of the cut-off low.

Three of the main numerical weather prediction models that we use in Australia each put the low in slightly different locations on Boxing Day.

This is the BoM's ACCESS-G model, showing the low positioned over northwest Victoria at 5pm AEDT on Boxing Day. Remember that air moves clockwise around a low in the Southern Hemisphere. So under this scenario, the air is being directed towards Melbourne from the northeast and this warm and moist airstream could help fuel showers and storms.

Image: Think of this one as a ball that doesn’t spin too much. So if the weather is the bowler and the crowd is the batter, the batter should still be very watchful. Source: BoM ACCESS-G.

Now here's the same time step from the ECMWF model (European Centre for Medium-Range Weather Forecasts). The low is centred over a more easterly part of northern Victoria, which could allow it to tap into more moisture-laden air from the Tasman Sea and convert it to heavy rain over southern Victoria.

Image: Think of this as a classic leg spinner. You know the ball is going to be tough to play. Source: ECMWF.

Now here's the GFS model (or Global Forecast System model, generated by NOAA in America). This one has the low positioned over South Gippsland and if the low is positioned far enough to the south, the day's worst rain and storms may occur to the south and west of Melbourne.

Image: Think of this model as a "googly" – the hardest ball for any batsman to pick. Source: GFS.

In short, unsettled weather is coming to Victoria on Christmas Day and Boxing Day.

To continue with our cricket analogy, we can't quite yet know exactly what the bowler is doing with their fingers and wrist position, and what sort of delivery is going to pop out. It all depends which model is the most accurate.

We'll keep you posted and urge you to keep checking our Melbourne forecast, which updates twice daily.