The only idea that is being supported by the general modelling that has shifted overnight is the stalling of the trough through Central SA, generally, the heavy rainfall and thunderstorm activity looks to hang up over the Eyre Peninsula, West Coast and through the Northwest Pastoral District.
If this does eventuate, there is some risk that areas in these districts could see their heaviest Summer rainfall in the absence of a tropical low, in more than half a century, so it is a significant system.
The showers and thunderstorms under that idea would struggle to move further east, so the YP, Adelaide, Mid North and Flinders may be on the edge of it for a while before the system eventually sweeps east next week through Australia Day or thereafter.
Rainfall Forecast Next 10 Days
Rainfall guide, largely unchanged, you may note that the heaviest of the rainfall has shifted further west and the banding of moderate rainfall becoming more narrow. That is due to the guidance tightening up. Heavy rainfall with thunderstorms will dictate who gets the biggest rainfall totals. However, even in areas slated in for 25-35mm of rain for example, there may be falls in excess of 50mm in a sitting. So use this as a guide. The heaviest rainfall leading to a flood risk is centred around the Outback, mainly west of the Stuart Highway through the NWP. The weather driest in the far west and over the far northeast at this time. Mixed odds for Adelaide and points east. Depends on whether the trough lifts eastwards, but it will be very humid.
Severe Weather Watch - Friday through Tuesday
Thunderstorms are expected to drive the severe weather risks from Thursday but mainly Friday and over the weekend and into early next week. Daily rounds of severe thunderstorms with heavy rainfall leading to flash and riverine flooding is the main concern at this time but large hail and damaging winds will also feature. Some locations could see rainfall totals exceeding the monthly average with one thunderstorm! And this likely to be repeated over a number of days, things could turn from very dry to flooded in quick time over the inland and about the western Ag areas. Significant storms will push east next week but there may be another wave of low pressure that forms later next week introducing thunderstorms back to the region identified here.
Flood Watch - Friday through Tuesday
Significant thunderstorm activity for a number of days over the same areas could lead to flooding for Outback areas of SA and extending into the Eyre Peninsula and possibly the remainder of the eastern districts, depending on the trough evolution and low pressure development. At this time the higher risk is for areas over the EP and points north and this may continue later next week with another wave of heavy moisture linking up with another trough.
Rainfall is the main issue with this event leading to significant risks of flooding as outlined above. There is also the chance of significant flash flooding and riverine flooding with a long duration period showers and storms. The heaviest of the rainfall will be determined by the location of the trough over SA and how quick it moves eastwards through the forecast. At this time, the outback areas between Glendambo through Coober Pedy up to Oodnadatta look to be the bullseye for heaviest of the rainfall but looking below, the trough rules.
12Z UK - Rainfall Next 7 Days
Can clearly see where the trough hangs up and produces round after round of showers and storms over the same area in SA, though the trough slowly moves eastwards next week. This will spread the rainfall through much of the Ag Areas. The grey and purple shading is showing rainfall of 200-300mm for parts of outback SA. I am not forecasting as heavy rainfall as this but certainly conceivable some areas could cop that much.
12Z ICON - Rainfall Next 8 Days
The trough not as deep but still has heavy rainfall of 100-150mm for outback areas of SA through to the Mid North and that rainfall coming into the Flinders as well. The trough is positioned a little further east through SA.
12Z ACCESS - Rainfall next 10 Days
Heavy rainfall attached to the trough over a similar position to UKmet, has heavier rainfall than the UKmet and Euro, with up to 300-400mm near Roxby Downs and heavy falls of 200mm through to the NT border.. This would lead to significant flooding along the Stuart Highway. The rainfall weakens on this product by the time it reaches the east and southeast Agricultural Areas as the trough stalls out.
12Z CMC - Rainfall Next 10 Days
Also showing heavier rainfall but takes the heavier rainfall through the EP, Flinders and Mid North back to the NT border with significant flooding possible and severe thunderstorms with damaging conditions if this verifies. The rainfall makes it to the eastern Agricultural areas but the weather is less amplified here.
So plenty to keep an eye on but for now, the confidence in the behaviour of the trough is low, but the confidence is creeping up on heavy rainfall developing for Central SA through to the NT border, along and to the west of the Stuart Highway.