October 2022 Update SA

                                                              October 2022 update SA

*Forecast prepared between October 17th 19th 2022]

Review:

G’Day everyone, apologies for the lateness in this mid-month update, had the wife’s 40th birthday on the weekend just gone by and it’s been a busy time getting the place looking tip-top, from painting the inside to getting the lawn like a bowling green. Then before you know it the day is over, and you are left with one big mess! But a great time was had by all and just now I've got some horrendous sciatica, wouldn’t wish it on my worst enemy so sitting and typing is not ideal, but the update must be sent out so standing and typing will have to do.

Now onto the weather and boy has it been active, a complete horror story for VIC and N TAS as well as large portions of inland NSW, especially just west of the Great Divide. Multiple strong upper troughs have continued to tap into tropical moisture from both the Indian and the Coral Sea, inducing surface lows and deep troughs on a classic rinse and repeat pattern with a peak in activity consistently over NSW and VIC but also affecting S QLD, N TAS and some portions of Eastern SA, chiefly the Riverland, Flinders and broader eastern border areas which really don’t need anymore rain in terms of cropping zones at least - it’s pretty rare to be saying that about these areas but alas a significant amount more is to come between now and the end of the year.

Meteorological Discussion:

I will try to keep this a little more concise because the Negative IOD and La Nina pattern combined impact is now beginning to reach a peak and as a result, many more strong upper troughs, cut off lows and broad thundery systems will occur between now and the end of the year, especially focused and enhanced over the eastern states where devastating flooding will occur with significant Murray and Darling flow rates not seen since 1974 – this outlook has not changed.

Firstly, I will cover SA and as of the evening of the 17th, we have an upper low that is pinched off from the westerly belt and become slow moving. At the surface this has begun to induce a deepening cut off low and these two features will combine together in the coming days to generate

widespread showers, thunderstorms and areas of rain, with heavy falls and inland flooding across the Pastoral areas, especially so around the Tarcoola to Woomera and parts of the Flinders. It honestly wouldn’t surprise me to see parts of the Stuart Highway cut from this but certainly any smaller roads will either be washed away or severely damaged. Granted the instability associated with this system, thunderstorms will be more frequent than previous events and thus more locally intense rainfall will occur. It will not take much to cause damage and some areas that copped enormous rain earlier in the year across the Southern NW Pastoral, will do so again.

Tuesday 18th

Areas of patchy rain will extend well eastwards ahead of the low-pressure system and weaken however closer to the apex of the upper low and the surface troughline, showers and thunderstorms will be ongoing across areas inland and north from the Nullarbor Plain, extending and developing eastwards during the day. Areas of messy patchy rain and decayed thunderstorm areas will extend across Eyre Peninsula, though mostly the northern portions with a cradling ridge to mostly keep the Lower reaches relatively dry with only minimal falls if any at all. Towards the afternoon, severe thunderstorms are likely to erupt along the troughline extending across the NE Pastoral up towards the NT border. I would expect these to contain damaging winds, large hail and intense rainfall with wind shear conducive to organised thunderstorms and this will continue into the evening from areas north of about Leigh Creek right up to the NT border with places such as Moomba and Innamincka especially at risk of such thunderstorms. Further south down to Port Augusta and west towards the Northern EP and Ceduna the showers and thunderstorms will tend more to areas of rain wrapping beneath the main upper level low.

I should also make note that the NE to E winds ahead of the low, especially on the western slopes of the Flinders will be very strong with squally gusts at times giving rise to damaging potential, similar to what Adelaide and surrounds experienced on the 4th. These strong NE winds also will make the inflow to any organised thunderstorms over the NE Pastoral conducive to producing tornadoes should a thunderstorm move into such an inflow environment but given the remoteness of the area, seeing one will be extremely unlikely unless one does indeed hit the aforementioned towns in the previous paragraph.

Wednesday 19th

The upper low and surface low combination will move slowly eastwards during Wednesday before gradually dropping SE and eventually south over the western portions of NSW due to a weakness in the cradling ridge to the south. Showers and thunderstorms will continue in a band sweeping around the eastern and lower side of the system, moving southwards and tending to a band of rain for areas

east of the Flinders and far northern Mt.Lofty Ranges, about as far south as the Riverland and a little patchier further west as a reverse rain shadow begins to take effect. Further north, much closer to the centre of the upper low across the NE Pastoral we will once again see surface heating result in scattered showers and isolated afternoon thunderstorms. Due to the cold air aloft, some of these may contain hail although the dynamics of these will be weaker than the previous day and thus smaller hail and smaller storms in general are likely.

Thursday 20th

Now the low will begin to weaken here and sag southwards across Western NSW to be centred somewhere near Pooncarie by the late evening. Scattered showers with isolated afternoon thunderstorms are still likely, being driven back west around the base of the upper low into the districts east of the ranges chiefly but also may rise up onto the ranges as well but be well shadowed on the western side. There is a chance of a severe thunderstorm closer to the eastern border as the upper levels cool with eastern extent with possible borderline large hail, intense rainfall the main threats but damaging winds a chance also if any microbursts form. Intensity of convective activity decreases west of the Murray River approximately.

Friday 21st

A case of rinse and repeat of the Thursday but with a southward movement of the weakening low over VIC, I’d expect the activity to also move south so the Lower SE will also be in the firing line. General scattered showers and isolated thunderstorms, chiefly afternoon and early evening on and more so east of the ranges. Seabreeze convergence may enhance thunderstorms in the afternoon.

Now beyond this we see what could potentially be the major cut off low I have been expecting this month, if it is not this system then the one after could also be significant though from a solar perspective, positioning is the only issue now - will it tend east again like a lot of activity has this season so far. In any case a slow-moving deep trough with strong upper-level forcing will induce a slow moving cut off low with widespread showers tending to rain, heavy at times as well as isolated thunderstorms, scattered in the afternoon about the Pastoral areas. This system will also be significant for NSW and VIC with multiple rounds of showers and thunderstorms with heavy falls and widespread flooding and massive areas of inundated property. I will most certainly issue a special update for this one covering all affected states.

We will see more deepening troughs out of WA with upper-level support although the strength of these depends a little on how the large event from 22nd-25th goes. An event from 29thh-30th seems possible at this stage with showers, thunderstorms and areas of rain with potentially more of a frontal connection resulting in colder air behind but wait and see as we get close, given the wild dynamics of the jet, the position and style of system are likely to be quite hard to place.

Climate Drivers

The Pacific continues to hold very firmly in a La Nina phase and given the strength of the trade winds and the cooler anomalies in the sub-surface in the east, I expect this to hold right to about December before we see some signs of weakening in the oceans. As a result, combined with the very war Coral Sea, expect more of the same over Eastern Australia (sounds like a broken record here!) with wet conditions and above average rainfall dominating including widespread flooding, especially over the Murray Darling Basin.

Figure 1: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/

The Indian continues to also hold firmly in the Negative IOD area with the Western Indian now cooled right off whilst the Eastern persists warm. I do think the warm area has started to extend west a little further offshore but certainly no cooling closer to home yet. The IOD is now at maximum strength and impact with numerous cut off lows and strong troughs developing as a result. It has also combined very well with the La Nina and together is creating a very dominating upwelling area over Eastern and SE Australia with the classic drier signature over SW WA.

Now the MJO is a little strange at this current point in time with a split pattern, refer to Figure 2. We still have an anchor of upwelling over the Eastern part of the mainland with more further east and downwelling over Africa. As this finally shifts east a little we may see a higher chance of a W/SW flow establishing behind all this troughing which at this stage I’d underpin for later in the month but granted how strong the La Nina and Negative IOD forcing is, the SAM will not have much time to swing negative at all, maybe neutral at the most before going straight back down to positive.

Figure 2: Current MJO from CHI200 – source Mike Ventrice http://mikeventrice.weebly.com/mjo.html

As just mentioned, the SAM has been positive for a while but will have a swing back towards neutral status at least allowing some colder air to push up late month, but this will not last too long as we return to highs getting crushed well south and inland troughing dominating in November for the most part allowing those humid and thundery conditions to prevail as I have mentioned in previous updates and outlooks

Districts:

Eyre Peninsula

Cut off low with areas of rain, chiefly north and east of the district on 18th before mostly clearing on 19th apart from isolated afternoon or evening showers in the far NE. Becoming mostly fine under the influence of a cradling ridge from the south until another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd, more frequent in the north and east once again before turning to areas of rain by the 23rd with moderate falls possible in the north and NE but minimal totals about the Lower Eyre Peninsula. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. Rainfall for the period 10-20mm but grading to 25-35mm in the north and NE potentially. Totals may decrease about the Lower Eyre Peninsula if the 29-30th system is weaker than expected but currently at least 8-15mm through there.

Upper North

Cut off low with areas of rain over the Flinders and mostly east and north of about Port Pirie on 18th. Isolated thunderstorms, chiefly afternoon over the Flinder with local heavy falls. Light areas of rain or mid-level showers extending back from the east on 19th however once again chiefly in the east of the district. Light patchy rain or mid-level showers again extending from the east on 20th with isolated afternoon thunderstorms possible in the far east. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with isolated showers and afternoon thunderstorms, chiefly about the ranges and east of the district. Another upper trough moves in

from the west inducing mid-level showers and isolated thunderstorms on the 22nd, more frequent about the Flinders with before turning to areas of rain and isolated thunderstorms with local heavy falls and possible flooding by the 23rd although lighter totals expected in the far west and SW of the district. A weak trough will likely pass north of the district on 25th, perhaps generating mid-level showers before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 15-25mm but grading to 30-40mm about the Flinders. Isolated heavy falls to 80-100mm with any thunderstorm activity. Totals may decrease about the south if the 29-30th system is weaker than expected but currently at least 10-15mm through there probably closer to 20mm.

Lower North

Cut off low over interior of state directing areas of patchy light rain on 18th. Light areas of rain or mid-level showers extending back from the east on 19th however once again chiefly in the far NE corner of the district. Light patchy rain or mid-level showers again extending from the east on 20th with isolated afternoon thunderstorms possible in the far east and also about the ranges. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with isolated showers and afternoon thunderstorms, chiefly about the ranges and east of the district. Another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd, with before turning to areas of rain and isolated thunderstorms with local heavy falls in the north and east possible on the 23rd although lighter totals expected in the south of the district. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 20-30mm but grading to 30-40mm in the far north and east. Isolated heavy falls to 50-60mm with any thunderstorm activity towards the N and E. Totals may decrease about the south if the 29-30th system is weaker than expected but currently at least 15-20mm through there probably closer to 25mm.

Yorke Peninsula

Cut off low with areas of rain, chiefly north and east of the district on 18th before mostly clearing on 19th apart from isolated afternoon or evening showers in the far NE. Becoming mostly fine under the influence of a cradling ridge from the south until another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd before turning to areas of rain by the 23rd. Slight possibility of some moderate falls about the north of the Peninsula although lighter totals are likely with southward extent towards the foot. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. Rainfall for the period 10-20mm

but grading to 20-25mm in the N potentially. Totals may decrease about the foot if the 29-30th system is weaker than expected but currently at least 5-10mm through there.

Kangaroo Island

Cut off low over interior on 18th although mostly only blow of cloud before mostly clearing on 19th. Mostly fine under the influence of a cradling ridge from the south with fresh SE seabreezes until another upper trough moves in from the west inducing mid-level showers and possible isolated thunderstorms on the 22nd before turning to patchy rain by the 23rd but at this stage, only light falls due to the ridge further SW holding the trough and low to the N and E. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. Rainfall for the period 5-10mm but grading to 20mm potentially if 29th-30th system develops properly.

Adelaide Plains

Cut off low with areas of patchy light rain, chiefly north and east of the district on 18th before mostly clearing on 19th to a sunny day. Mostly fine under the influence of a cradling ridge from the south although on 20th we may see an isolated afternoon shower about the outer N plains with the low to east moving south. This may repeat on 21st with a little more intensity and spread before ceasing in the evening. Another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd before turning to areas of rain by the 23rd. Slight possibility of some moderate falls about outer northern plains although lighter totals are likely with southward extent towards the Fleurieu. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. Rainfall for the period 10-20mm but grading to 20-25mm about N plains potentially. Totals may decrease towards the southern Fleurieu if the 29-30th system is weaker than expected but currently at least 8-15mm through there.

Mt.Lofty Ranges

Cut off low with areas of patchy light rain, chiefly north and east of the district on 18th before mostly clearing on 19th to a sunny day. Mostly fine under the influence of a cradling ridge from the south although on 20th we may see an isolated afternoon shower about the N ranges and moreso eastern slopes with the low to east moving south directing that easterly moist flow towards the west. This may repeat on 21st with a little more intensity and spread with an afternoon thunderstorm possible

about the eastern slopes before ceasing in the evening. Another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd before turning to areas of rain by the 23rd. Slight possibility of some moderate falls about outer northern ranges although much lighter totals are likely with southward extent towards the Fleurieu. A weak trough will likely pass north of the district on 25th before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. Rainfall for the period 10-20mm but grading to 20-30mm in the N potentially. Totals may decrease about the foot if the 29-30th system is weaker than expected but currently at least 8-15mm through there.

Riverland/Mallee

Cut off low with areas of patchy light rain on 18th. Light areas of rain or mid-level showers extending back from the east on 19th however only grazing the far N Riverland. Light patchy rain or mid-level showers again extending from the east on 20th with isolated afternoon thunderstorms possible about the Riverland and potentially Eastern border of the Mallee. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with isolated showers and afternoon thunderstorms., again more focused closer to the eastern border. Another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms on the 22nd, about the Riverland with before turning to areas of rain and isolated thunderstorms with possible local heavy falls over the far N/NE Riverland by the 23rd although lighter totals expected as we move south and SW through the Mallee District. A weak trough will likely pass north of the district on 25th, before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 15-25mm but grading to 25-35mm about the far N Riverland. Isolated heavy falls to 50mm potentially with thunderstorm activity. Totals may decrease about the southern Mallee if the 29-30th system is weaker than expected but currently at least 8-15mm through there probably closer to 15-18mm.

Upper SE

Cut off low inland with areas of cloud increasing on 18th and 19th. Light patchy rain or mid-level showers extending from the east on 20th with isolated afternoon thunderstorms possible in the north and potentially Eastern border. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with isolated showers and afternoon thunderstorms, again more focused closer to the eastern border. Another upper trough moves in from the west inducing light patchy rain early on 23rd. Re-circulated moisture from the back side of the secondary low over VIC may push light rain areas or showers back west from VIC late 24th and early 25th. A weak trough will likely pass north of the district on 25th, before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 10-15mm but grading to 15-20mm about the far N of the district. Isolated heavy falls to 25mm potentially with thunderstorm activity. Totals may decrease about the Coorong coastline if the 29-30th system is weaker than expected but currently at least 5-10mm through there probably closer to 10-15mm.

Lower SE

Cut off low inland with areas of cloud increasing on 18th but remaining fine. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with isolated showers and afternoon thunderstorms, again more focused closer to the eastern border but assisted by seabreeze convergence. Another upper trough moves in from the west inducing light patchy rain early on 23rd. Re-circulated moisture from the back side of the secondary low over VIC may push light rain areas or showers back west from VIC late 24th and throughout 25th with potentially fresh to strong SE/S winds around the back side of the low, especially so about exposed coasts. A weak trough will likely pass well north of the district on 25th, before a ridge quickly establishes behind. Yet another deepening trough 29th-30th bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 15-20mm but grading to 20-25mm about the far E of the district. Isolated heavy falls to 30mm potentially with thunderstorm activity. Totals may decrease about the western coastline if the 29-30th system is weaker than expected but currently at least 5-10mm through there probably closer to 10-15mm.

Western VIC

Cut off low developing over N SA from 18th but remaining fine. Light patchy rain or mid-level showers again extending from the NE on 20th with isolated afternoon thunderstorms possible about the Mallee. Remaining fine over the SW District most likely. As the low moves south, moisture and instability will direct up more from the SE to S on 21st with scattered showers and afternoon thunderstorms, possibly severe during the afternoon with local heavy falls and hail possible. Another upper trough moves in from the west inducing mid-level showers and isolated thunderstorms possible about the Mallee late 22nd or early 23rd before thickening to areas of rain and isolated thunderstorms during 24th and 25th and extending back down from the NE as a low deepens and moves S to SSW. Local heavy falls possible again with flooding possible in the far E and NE of all districts of Western VIC. A ridge quickly establishes behind on 26th to 27th thereafter. Yet another deepening trough 30th-31st bringing scattered showers and thunderstorms from the west. This may also tend to rain areas. Rainfall for the period 25-40mm but grading to 40-60mm about the far NE and E of the districts. Isolated local totals to 90mm potentially with thunderstorm activity and persistent heavy rain areas. Totals may decrease about the far W near the SA border if the 29-30th system is weaker than expected but currently at least 15-25mm through there.

Finals Notes:

• Widespread and historically significant major flooding to increase across NSW and VIC but also parts of QLD and TAS.
• Significant river flooding from upstream flows to occur along the Murray in SA, with levels expected to reach close to 1974 at this stage
• Inland flooding likely across both the NW and NE pastoral especially from heavy rainfall and these events will continue with more thunderstorm activity in November.
• Less impacts the further west and SW one goes; however these districts will still see an increase potential for rain and thunderstorm activity for the remainder of the year with increased humidity feeding in from the NE and N.
• Negative IOD and La Nina combining with force to deliver repeat upper lows and cut off systems with large cloudbands and powerful uplift through the rest of October and November
• Slight tapering in December in SA as Negative IOD wanes but Eastern states likely to continue to see widespread flooding and unfortunate devastation to crops, homes and infrastructure
• Easing of the worst through early 2023 with heatwaves likely through Jan and especially Feb

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

Happy Farming and Cheers from The Weatherman

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