MODELS AND THE RAINFALL - ALWAYS GOOD TO LOOK AT THE BROADER DATA SETS THAN THE APPS.

The apps are causing people some grief, so lets break down the latest details of what you need to know in the short, medium and longer term.


There is a bit to unpack as the weather does turn in the medium term and there are a few solutions that have got me concerned for further flooding again so please read the blubs and risks so you can track where I am going with the forecasts into the medium term, making it easy for you to pop in and out and pick up the changes as they develop.


SHORT TERM

One trough has now passed into the east and will stall out over inland QLD and northern NSW, this will stay in place. Another trough is deepening over WA and that is forecast to pass into the south and then southeast this weekend, producing more rain and thunderstorms over the southeast and east of the nation. The coverage of rainfall out west is expected to be mainly light with the unstable air, thanks to limited moisture. The tropics expecting to see more rainfall from later this week into the weekend with a trough forming.


UKMET - Rainfall Next 7 Days - HIGH CHANCE

No change once again from yesterday and the coverage of rainfall is fair. The intensity will vary from location to location thanks to the thunderstorm risk in the mix.

MEDIUM TERM

This is where the modelling is struggling with the timing of the shift to wetter weather over northern and eastern Australia and it comes down to two elements. 1, being the position of the new ridge over Christmas, does that track further south or sit further north as it is this week? 2, do we see a unstable westerly flow develop over northern Australia, not quite monsoonal westerly winds, but a shift that allows moisture to be projected southeast and east across the tropics? The wildcard in this period is the development of a low pressure system over northern Australia and this tracking south towards the nation and this propelling more moisture over the nation, lifting rainfall chances as the troughs deepen over the western, eastern and northern inland of the nation


ICON - Rainfall Next 8 Days - LOW CHANCE

Still off with the fairies but it is important to show you. Way too dry.

CMC - Rainfall Next 10 Days - MODERATE CHANCE

The CMC is reflecting the shift to more rainfall over northern Australia resulting in more moisture being drawn south into troughs over WA, then into troughs through QLD and into northern NSW. But the model is suggesting that the high pressure system to the south will continue to hold out the rainfall until after Christmas for the southern and southeast states at this time, while remaining hot and humid.

EURO - Rainfall Next 10 Days - HIGH CHANCE

Rainfall is increasing gradually over northern Australia, watching the hints of a tropical wave orgainsing into a low pressure system offshore the NT or WA with moisture from that feature spreading southeast and east across the nation. Watching the east coast with the return of easterly winds and showers and that moisture being fed into troughs over central QLD and northern NSW. The west remaining dry and hot with the inland trough struggling with limited moisture and the south and southeast dry, refer to the Ensemble data sets to see what happens after Christmas.

ACCESS - Rainfall Next 10 Days - MODERATE CHANCE (only because of the tropical moisture up north).

Again a little too aggressive on the spread of rainfall this side of Christmas, I think that at this time, a lot of this will fall from Christmas onwards. Uneven rainfall expected through the coming 7 days with the most scattered falls expected for the northern tropics and through the eastern inland of QLD down into NSW and the ACT with a number of troughs passing through. The tropical north is the area to watch with that tropical wave passing through over Christmas possibly becoming more organised into something more substantial.

KMA - Rainfall Next 12 Days - LOW CHANCE

It has been volatile the past few days and remains so tonight, though it is pinging more moisture is in play through next week and from Christmas onwards which is correct, the distribution is off.

GFS - Rainfall Next 16 Days - LOW CHANCE

Refer to the ensemble data below but this particular run is way too dry for the south, however 3 out of the past 6 runs have shown major rainfall events sweeping the nation in the period after Christmas.

ENSEMBLE DATA

These sets have been much more reliable and settled in the idea of rainfall becoming more widespread. The broader data sets swaying in line with the idea of the weather getting wetter and more humid as we go from Christmas into 2022.


GFS - Rainfall Next 16 Days (median of 35 members) - LOW CHANCE

This is much wetter than the determinstic you can see above, and the rainfall is expected to be driven by what occurs over northern and eastern Australia, in combination as to how far north or south the high pressure sits - this allowing the return of easterly winds across the nation or not. The members are split on these ideas hence the volatility. It has tonight extended the rainfall inland over QLD and NSW a little more.

CMC - Rainfall Next 15 Days (median of 30 members) - MODERATE CHANCE

This solution along with the Euro is likely the right solution under the current guidance from the Climate drivers.

EURO - Rainfall Next 15 Days (median of 51 members) - MODERATE CHANCE

Similar to last night, the weather will get wetter post Christmas from the north in line with the increase in tropical moisture, easterly winds and deepening inland troughs fuelling showers and thunderstorms and the high chance of more widespread rainfall events.

The broader data set showing the increase in tropical moisture this evening heading further south.

LONG TERM

These remain wet with above average rainfall expected, especially for the final 4 weeks of the outlook period for both sets.


GFS - Rainfall Next 5 Weeks - MODERATE CHANCE

It is gradually getting wetter over the north in line with the other models.

CFS - Rainfall Next 6 Weeks - MODERATE CHANCE

And we are back to square one over the east and southeast with well above average rainfall which is connected to the monsoon returning over the north. So the flood risk is not over.

The broader data set also agrees in this idea.

More coming up from 7am EDT.