SA - FINALLY CENTRE STAGE WHEN IT COMES TO THE RAINFALL CHANCES THIS WEEK

The wet weather has bypassed SA all Summer. Well not this week coming, and it looks like it could make up for the lost time with many areas looking to record their heaviest Summer rainfall in decades. Outback flooding a major concern. For transport and logistics running the Stuart Highway, you need to be paying attention to the forecasts with some roads likely to be cut in and around central and northern SA.


For Agricultural Areas, also pay attention to forecasts as a wobble of the trough to the southeast or northwest may make all the difference in rainfall projections. Some areas could see heavy rainfall but that is dependent on the track of the trough which may sit to the west of the region or close enough to spawn repeated bands of showers and thunderstorms. It is really a forecast that is on a knife edge. The impacts very high.


Lets get straight into it.

FORECAST

Rainfall Next 10 Days

Rainfall extensive, heavy and persistent across interior parts of SA which will lead to areas of flooding. Severe thunderstorms will dictate the terms of who gets the heaviest of the rainfall throughout the remainder of southern and eastern SA, and the trough will decide when that will be. So there are many moving pieces, each with consequences that are high impact. The bulk of the severe weather should start to migrate out of Central SA during early next week and relocate into VIC and NSW....but some models do keep the trough in place for a while longer, so that makes it hard to forecast the eastward progression of rainfall. For now, a wet and humid week for northern, central and then eastern areas. The heaviest of the rainfall likely over central and northern areas at this time.

Thunderstorm Forecast Thursday

Thunderstorms are likely to develop in response to an upper disturbance moving northeast from the Bight and tapping into copious moisture. This will lead to widespread showers and thunderstorms developing with some of the storms possibly severe, with heavy rainfall leading to flash flooding the main risk. The severe thunderstorms are more likely during Friday and across the weekend.

Flash Flood Risk Thursday

Thunderstorms will be developing in a very rich moist environment, perfect for high precipitation cells. Thunderstorms carry a high risk of producing flash flooding over northern and central inland areas, mainly west of the Stuart Highway.

DATA - Refer to video for more information on the daily breakdown


00Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 16 Days

As mentioned in the video above, the features to watch are the trough over SA, does that stay stationary, bringing heavy rainfall for multiple days over central SA through to the NT with flooding a high risk, or does that trough weaken or does it move east? This will dictate weather over the central and eastern parts of the nation and this is what models are struggling with. The GFS keeps it stationary. Very humid air and stable weather for the eastern inland of the nation with above average humidity values will make things feel pretty foul. Showers and thunder for the east coast in onshore winds, some of those could be heavy for NSW and southeast QLD. The tropics, the feature to watch is the monsoon trough and whether a low pressure system forms in the trough. If it does develop, does that form near WA, NT or QLD? Models have diverged on that idea as pointed out today, that too has a major impact on rainfall and moisture forecasts moving forward. Finally, the SAM, does that turn neutral allowing the west of the nation to cool down for a number of days thanks to the westerly wind belt moving north. Does that westerly wind belt flush the humidity north? Plenty of moving pieces and sadly more questions than answers right now.

00Z GFS - Precipitable Water Values - Next 16 Days

As mentioned in the video, a very rich and broadly moist airmass will result in high rainfall chances for the nation, and where troughs form, flash and riverine flooding is possible for many areas through this period. The monsoon over the north looking to crank as well, and that will add more moisture to the nation meaning a wet end to January and start of February.

00Z GFS - Rainfall Accumulation - Next 10 Days

Refer to video for further details

00Z CMC - Rainfall Accumulation - Next 10 Days

Refer to video for further details

00Z GFS - Rainfall Accumulation - Next 16 Days

Refer to video for further details

A closer look in - the rainfall through outback areas could exceed 200mm from this first event, regardless of what models say. Thunderstorms will be efficient rainfall producers. Some areas could get 50-70mm in an hour and then areas of rain with moderate falls surrounding these large thunderstorm clusters.

More coming up after 9pm EDT with a look at the models and the rainfall forecasts. Very much a divergent bunch of data right now.


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