Not very often do you see such extensive heavy rainfall as what is forecast for central and northern SA. Some areas could see a year's worth of rainfall, this being equivalent to a 1/50 year event for inland areas of the state.
The worst of the weather may sit north and west of Adelaide, but may impact areas over the Eyre Peninsula, especially northern and western parts, may drift into the Mid North and Flinders as well.
High humidity and thundery weather will eventually fold over the remainder of the southeast and eastern districts but the dynamic support for severe weather may be reduced as the trough weakens. The overall confidence in the evolution of the system is not especially high, with some modelling suggesting that the trough will have a low pressure system form on it, others saying no.
Medium term, there are strong signals that a repeat event may develop from later next week with another impulse of moisture from the tropics, the monsoon influencing the weather for a lot of the nation. With high pressure systems staying to south, it is open slather on the nation being caked in moisture for a while. So heads up for the short and medium term severe weather risks.
Rainfall Next 10 Days - Agricultural Areas
Extensive heavy rainfall is expected to emerge out of the thunderstorm activity that is already underway through the Northwest this morning. The rain repeating over the same areas over the course of the next 4-5 days with heavy falls, severe thunderstorms and a flood risk that will drag on for multiple days. The rainfall focus will shift very slowly to the east and southeast through the coming few days, with scattered showers and thunderstorms eventually spilling over to the eastern districts. Another trough may reform over the western districts mid to late next week with further heavy rainfall and thunderstorms possible over the same areas again.
Thunderstorm Forecast Friday
Thunderstorms are expected to be ongoing from tonight through Friday, with severe thunderstorms highly likely. Heavy rainfall leading to flash flooding the main concern, there may be intense bursts of rainfall through the Outback leading to very nasty flooding. Damaging winds and large hail also a risk as well on the periphery on the main area of thundery rainfall band and heavy cloud cover.
Flash Flood Risk Friday
A very high risk of flash flooding through a large area of the outback with life threatening flash flooding possible.
Damaging Winds Risk Friday
Damaging winds are expected with thunderstorms that form on the edge of the cloud band. This is where the air will likely be warmer and more unstable.
Large Hail Risk Friday
Similar to above, the large hail risk found on the periphery of the cloud band but mainly in the western and northern aspects of the cloud band.
Riverine Flood Risk Friday through Tuesday
A very high risk of riverine flooding throughout large areas of the Outback with roads and communities cut. Some areas could see flooding for weeks as a result of this first event and the risk may be exacerbated by the secondary feature mid to late next week IF that does indeed verify, but we need to flag that.
18Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 7 Days
A stagnant pressure pattern over SA with a deep trough and very deep moisture profile in place, will lead to widespread showers and thunderstorms, locally heavy rainfall and flooding risks from today through to about next Thursday over the same region. This is expected to lead to not only above average rainfall but the risk of record rainfall for January. Some locations could lead to a years worth of rainfall in a sitting. The weather pattern starts to break down from a week from now with the moisture set to move east and north, but in the medium term beyond this, the weather may turn wet and stormy again over this same area, so will keep an eye on the trends. But this first system looks to be a cracker.
18Z GFS - Precipitable Water Values - Next 7 Days
Record moisture profile in place for the coming week spells a very wet period for SA, with the trough anchored over central and northern areas, that is where you will find the wettest and most severe weather. The moisture will eventually get kicked out to the east and north in about a week as the trough moves on by.
18Z GFS - Rainfall Next 7 Days
Latest GFS has the heaviest of the rainfall over the EP and points north and west. It is not as amplified as other models but some areas could record falls over 150mm through this period. Note the rainfall gradient turns lighter over a shorter distance as you move eastwards. This is because rainfall is moving from northeast to southwest over the same area.
18Z ICON - Rainfall Next 7 Days
Has the trough a little further east than GFS and this rainfall is expected to be heavier over the EP and Mid North and Flinders if this verifies. Moderate to heavy rainfall would then be able to form further east under this solution.
12Z Euro - Rainfall Next 7 Days
Heavy rainfall of 50-150mm over a wide area from the West Coast, through the EP through the Flinders and into the NEPD. Some areas could see falls over 200mm through this period. Lighter falls east with the trough stalling out over the central inland.
12Z CMC- Rainfall Next 7 Days
This is the most aggressive on the rainfall front. Some areas could see 200-300mm in the coming week with the trough stalling out over the EP and West Coast and extending the heavier rainfall north to the NT. Flooding a very high risk. Lighter falls east with the trough remaining stationary to the west, so points from Adelaide eastwards to see patchy falls and high humidity.
More details to come this evening.