Quick Update VIC SA upper lowtrough with showers and thunders

Quick Update VIC & SA upper low/trough with showers and thunderstorms April 1st 2024

G’Day everyone, thought I’d whip out a quick little update tonight just to cover the developing situation for tomorrow over much of Western to Central VIC and some far eastern portions of SA – mainly the eastern and northern Riverland but also potentially eastern border regions of the Mallee also but the main focus is well and truly in VIC.

Today on March 31st (Easter Sunday) we have seen some afternoon and evening showers and thunderstorms develop with surface heating, primarily over the ranges north and NE of Adelaide across both the Lower and Upper North as well as the Flinders. Later near sunset some of these developed down across the Riverland and Northern Mallee before petering out. Locally heavy falls with flash flooding have occurred. Yesterday on the 30th (Easter Saturday) we saw some more significant thunderstorms in slack shear and deeper moisture develop across the NE Pastoral with some localised intense rainfall and flash flooding. I have seen reports of 179mm in some mining sites near Moomba with Moomba Airport itself recording 55mm.

Now the main take home is that we have a solid infeed of deep tropical moisture coming down from the NT and QLD cutting across the NE/E of SA, W NSW and into NW/W VIC through a warm and increasingly humid N airstream. So far only a weak surface trough has been lifting this moisture but for tomorrow (1st) a strong and fairly sharp upper low will stand up from the SW and rapidly increase the lift and upper divergence to the east of it. This system will combine with both the surface trough and moisture to generate an unstable atmosphere in which widespread showers and thunderstorms will develop, with scattered severe thunderstorms.

Initially, the thunderstorm activity will be elevated or higher based across far E SA border areas and mostly western VIC, chiefly in the SW District to Wimmera but as the day wears on into the afternoon, surface-based heating will cause a line of severe thunderstorms to erupt along the main troughline, extending NNW up through the Mallee and towards roughly the Renmark area of the Riverland. With the extra wind shear and lift from the upper trough, there is a good chance of supercell thunderstorms capable of large hail, damaging winds and very intense rainfall. These storms will become more linear in nature as the day wears on into a general line or possible squall line of sorts before tending to thundery rainband further east and a more embedded mode/spread out as the outflow takes over reducing the severe threat, but increasing the spread of good rainfall. Thunderstorms will continue to be fresher towards the far N end of the band as the evening wears on as the top of the line builds well into NSW.


Figure 1: 500hPa (~18,500ft) chart from ECMWF for 4:30pm ACDT showing the strong upper low approaching from the SW of Kangaroo Island – source Meteologix


Behind the main troughline back in SA with the upper low influence, some showery bands will develop with a lower risk of severe weather, but perhaps some stout showers at times and perhaps an isolated thunderstorm or two with a small hail risk. This is most likely over the Lower SE District closer to the colder air but also possible anywhere up to about the Lower North District including Adelaide. A fresh to strong SW flow will follow with some stream showers across Southern ag areas as a surface low develops south of VIC and a strong new high pushes in from the west, squeezing the isobars together.

Rainfall totals will be quite spasmodic and isolated the further west one goes and especially west of about the Grampians. Further east as one ventures towards Central VIC, the totals become more consistent. In any case isolated to scattered 5-15mm totals west of the Grampians and up to the NW corner. Localised 20-40mm rapid falls in thunderstorms towards the Eastern half of the Mallee/Wimmera and SW District with extreme 50-70mm dumps possible in more severe

thunderstorms or areas that receive multiple cells. More general 20-40mm totals as thunderstorms spread to rain over Central VIC, but isolated 50-70mm falls are still possible here also.

Back in SA, most totals will be hit and miss but cells in the N/NE Riverland have potential for rapid 20-30mm dumps. Less than 5mm for most other areas in the onshore flow and showery bands/colder air.

Hopefully no damage tomorrow but certainly a welcome drink for some of those dry areas in Western and certainly Central VIC. Good luck to all!

Link to temporary blog website: https://farmweathersa.blogspot.com/

Happy Farming and Cheers from The Weatherman

*Note – For interest only, all thoughts are of The Weatherman and may not be reproduced without my consent.

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