Quick Update SA Trough and cold front with rain/shower April 26th-29th 2023

Quick Update SA Trough and cold front with rain/showers April 26th-29th 2023

G’Day everyone, as promised a quick update before this next system. Now certainly since the April update, the overall vigour and northern penetration of the system has dropped off and we can thank the power of the Tasman high for that, with a firm ridge over the the top of the system deflecting it further south rather than some ridging cutting underneath it to lift it up. This will have a double edged impact however with the lead system becoming absorbed into the westerly belt quicker, it will then allow a second trough to sling up with an upper trough aloft with a bit more ease, as one goes down the back one comes up, rotating around a broader area of low pressure.

Wednesday 26th

A warm day for most districts with freshening N winds, tending warm to hot across the Northern Agricultural and inland portions of Eyre Peninsula up to the West Coast ahead of a trough and weakening cold front generating a band of rain and isolated thunderstorms. The top portion of the band will thin out to more of a broken band of showers with a distinct sliding movement and lack of penetration for inland areas. Isolated thunderstorms are more likely to be confined to the Bight area and adjacent Southern coastal portions of Eyre and Yorke Peninsula as well as Kangaroo Island.

The band of rain should reach Eyre Peninsula’s coastline by approx 3:30-4pm though more isolated cells may develop ahead of and north of it with reasonable warmth and dynamic lifting aloft generating some slight instability. The band should extend E/SE and reach the Adelaide region by about 8:30-9pm but continue a sliding pattern towards the eastern and SE districts. Due to this sliding action caused by the over-powering steering ridge to the east, areas north of a rough line from Ceduna to Cleve to Port Wakefield to Pinnaroo will see more convective and isolated precipitation with a thickening as one goes southward down the band. The further north one ventures, the greater the chances of no rain at all unfortunately, especially anywhere north of about Port Augusta to Renmark. One hallmark of this season as mentioned in a previous outlook/update is that Goyders Line will play a significant part, especially as time goes by after multiple fronts etc, we will start to see a clear trend here in terms of northward penetration so unfortunately this time, the Lower and especailly Upper North/Riverland and Mallee will feel a little hard done by however fortunately we have at least had some rain this season so any top ups will at least be useful for now.

Thursday 27th

The weakening first band will continue to slide ESE bringing that band of rain across the Upper and Lower SE from the early hours, with more isolated to scattered showers for the Mallee and very isolated showers for the Riverland, especially the N and E portions. A clearance behind the first system will ensue with a fine but partly cloudy day for most districts however in the Bight, the original deep low spiraling in from the west will weaken and approach the coastline generating an increase in showers for the Western coast of Eyre Peninsula and lower portions of Yorke and the Fleurieu and also most of KI however a lot of this activity will be light and insignificant totals wise, a mere wet the ground a bit with an increase in winds before the whole surface feature lifts and gets absorbed into the NW-SE flow and dives away to the SE also.

However as one slides SE, another on the pivot around the broader low pressure area will come up from the SW with a cold front due to arrive onto the West Coast of Eyre Peninsula by around 11:30pm with a band of showers.

Friday 28th and early Sat 29th

The cold front will move easteards across the southern agricultural area reaching Adelaide just before sunrise and continue on and ENE track giving a better chance of precipitation to areas that missed out with the first band.

Another clearance should occur however during the afternoon and evening, an upper trough with a pool of cold air aloft will push in behind the first front generating more convective showers, some potentially locally heavy with this having a little bit of inland penetration north of Adelaide but overall, the showers will still be fairly scattered and not widespread and be well shadowed by any terrain/ranges due to a bulk of it occuring at night where a lack of thermal warmth will temper the development anywhere beyond windward slopes.

Showers will quickly become isolated by daylight on 29th as a new ridge begins to muscle in maintaining a cool SW flow across the state.

Beyond this, a series of weak troughs will approach the state from the SW from 30th to 2nd which but mostly lack the penetratrion apart from isolated to scattered showers about the coastal portions of the Southern Agricultural area, namely KI especially.

Rainfall:

Rainfall for this system will primarily be strongly biased to the southern coastal regions and Mt.Lofty Ranges. Totals are up until 9am on 30th.

Eyre Peninsula:

General 5-8mm with isolatedtotals to 15mm about Lower Eyre Pen. Totals decreasing with N and NE extent of less than 2-5mm about NE Eyre Pen.

Upper North:

General 3-6mm with isolated 6-10mm about elevated windward slopes. Totals decreasing markedly with shadowing off the back of the ranges and to the far N in the order of 1-3mm.

Lower North:

General 5-8mm falls, with isolated 8-12mm totals about windward slopes and elevated terrain. Totals decreasing off backs of rangesmarkedly down to 2-5mm.

Yorke Peninsula:

General 5-10mm falls, with isolated 10-15mm totals, primarily about the foot. Totals decreasing towards the N in the order of 3-5mm.

Kangaroo Island:

General 10-20mm falls. Isolated 25mm totals about the western end and in any areas that may receive repeat convective precipitation.

Adelaide Plains:

General 7-12mm, with isolated 20mm totals possible closer to the foothills. Totals decreasing towards the outer N plains down to 5-7mm.

Mt.Lofty Ranges:

General 8-18mm, with isolated 18-30mm, more likely about known wetter portions of the southern Fleurieu. Totals decreasing markedly off the backs of the ranges down to 5-7mm.

Riverland:

A real struggle. General 1-2mm, isolated 5mm totals possivle towards the SW/W Riverland. Totals decreasing to less than 1mm in the north and east with some areas potentially recording a mere trace.

Mallee:

General 3-5mm, isolated 5-8mm possibly in the far south/SW but totals markedly decreasing towards the RIverland and eastern borders in the order of 1-3mm.

Upper SE:

General 5-10mm, with isolated 10-15mm totals towards the far south.Totals decreasing over the far NE corner of the district to 3-5mm.

Lower SE:

General 7-12mm with isolated 15mm totals towards the coast. Totals decreasing however in the far NE down to 5-7mm

Western VIC:

General falls of 5-10mm about the SW District and Southern Wimmera. Isolated 10-15mm totals possible about higher peaks near Grampians but a marked decrease towards the Mallee, and especially N malee in the order of 1-3mm with next to no rainfall or a trace towards the NSW border. Link to temporary blog website: https://farmweathersa.blogspot.com/

Happy Farming and Cheers from The Weatherman

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