October 2022 outlook SA
October 2022 outlook SA
*Forecast prepared between October 1st 3rd 2022
Review:
G’Day everyone, hope you are keeping well and have enjoyed the last couple of months with the boost in rainfall. We now approach a critical month in the grand scheme of things, with the potential for significant events as mentioned from the last couple of updates.
Firstly though, a look back at how September panned out and it was great to see a wet month for the most part across the state as expected. Numerous regions received above average rainfall but no doubt the best performed areas were the Riverland, Eastern half of the Mallee and the southern NE Pastoral – areas that have struggled for good rainfall for a very long time.
The most significant rain event occurred during the evening of the 20th with a substantial rainband mixed with isolated thunderstorms sweeping SSE before getting the pivot and coming back the other way before weakening. Numerous stations received 24hr totals in the order of 25-35mm with some closer to 40mm – a truly fantastic soaking rainfall for September which has no doubt boosted many marginal crops to very good to excellent levels by the standards usually seen in the Riverland and Eastern Mallee and border areas. Renmark received 35.6mm, Loxton 32.6mm after also receiving a very similar rainband of 20-30mm on the 7th. Overall, for the month Renmark received 84.2mm which is more rainfall than it sometimes receives in an entire growing season. Loxton came in at 79.2mm which is also excellent.
For the most part, the feeding of moisture on the NE stream ahead of cut off lows made a big difference rather than relying on frontal moisture which simply doesn’t do enough for these areas. Moisture from the warm Coral Sea greatly assisted this. But to put things into a picture, refer to Figure’s 1-3 below:
For reference, here is the September outlook:
“Overall though my outlook for September is for average to above average rainfall. It is the month most likely to exceed the mean though October may be similar. A good chance of well above average rainfall across the NE Pastoral, Mallee, Riverland, Upper North with a tapering to above average over the Adelaide and Mt.Lofty Ranges. The SE Districts should do well too. The greatest chance of below average rainfall is essentially nowhere at all, Western Eyre Peninsula would possibly be the only spot that may just sneak under but that’s a long shot. Looks a very wet month overall. So, no changes from the previous months outlooks with September being a peak month rainfall wise.”
I think overall, the month came off really well with the expected wetter trend to the eastern districts and NE (the Riverland especially did super well!) with an easing off towards the west with that little drier spot off Western EP/West Coast District. The Pastoral zone were a smidge drier in the middle though the mean is quite low so very small values less than 10mm make a world of difference.
Meteorological Discussion:
We now enter a period where a lot of powerful systems will develop across the country. For the most part, September was one of the coldest on record, just warmer than 1992 (which was much wetter than what we have just seen). The main focus for October is going to be the Eastern states with devastating rainfall to be blunt. Multiple upper trough and cut off low interactions channelling in warm, moist air from the Coral Sea will be a feature as well as moisture off the Indonesian area from the Negative IOD. As mentioned in previous updates, there will be widespread flooding and to be honest I think I underdid the level of what we could see over NSW in particular but also parts of VIC and Southern QLD.
Over the coming 2 weeks till roughly mid-month, I would expect widespread 40-80mm totals across inland NSW with scattered falls to 100mm and some isolated mammoth totals in excess of 150-200mm. This also could extend into Southern QLD. N to NE VIC will experience similar conditions but perhaps more general 30-50mm falls with some scattered totals to 75mm and isolated 100-125mm falls over the alps and catchments. It will be very, very wet.
The Darling is currently flowing strongly with 16 moderate flood warnings for either itself or tributaries that flow into it. Two of these were major only 24hours ago with a slight easing. The Murray currently has 12 moderate and 2 major flood warnings for either itself or associated tributaries that flow into it. As of September 14th, the total holdings of the Murray-Darling Basin were at 97%. Including the spilling of the largest dam in the country with Lake Dartmouth. With a combination of further significant rainfall events across the basin, snow melt and the trump card of the Coral Sea providing the potential for unusually intense and heavy rainfall, I can see many more rivers going into moderate to major flood with numerous townships being inundated and cropping fields flooded over vast distances as floodplains fill right up. The flow levels into SA are likely to be some of the most significant since the 73-75 period by the time all this is done as there is simply no more room for soils and river systems to absorb and contain new inflow. I don’t think we will reach 1974 levels but perhaps somewhere in the order of between 1973 and 1975 in terms of flow volumes and water levels. A good indicator historically is the Loxton Tree of knowledge which many of you may be aware of, certainly those in the Riverland at any case. There is also a similar tree in Swan Reach and Mildura from memory though nowhere near as detailed. I remember standing at the tree looking up at the various levels and being blown away by how high 1956 was. We certainly won’t be going that high, but it shows what can happen when there is a lot of water upstream (and locally) to enter the river system. Refer to Figure 4 below:
So, in summation, expect some significant flooding and river flows over the coming 2-3months, probably peaking sometime in either November or December before an easing trend into early 2023. Any shacks or properties along the Murray that have been flooded in 1990, 1991, 1992, 1993, 2011 & 2016 etc will be flooding again and likely many others higher up so please take heed. A quick look west towards WA sees a much drier story with the negative IOD having it’s usual influence there with a reduction in rainfall. There will be some fronts and troughs till mid-month, but a lot of the activity will be chiefly south of about Perth or the northern Perth area. Totals will also drop off behind the ranges into the wheat belt although 15-25mm is still a possibility. I do not envisage the harvest issues in WA that will plague areas in the eastern states and to some degree in SA.
Back to our expected weather though and certainly October should have no shortage of systems out of the NW in a strong meridional pattern with an expectation of numerous strong upper troughs to create cut off lows deepening out of inland WA as well as forming from cold fronts. A complex mixed bag and it could well end up even wetter than September in some parts, especially so for the interior as tropical air begins to feed in.
To begin with we finally see some much-needed warmth! As I type this on a sunny Sunday afternoon, the current temperature is 24.8C with some surface-based Cumulus developing over the ranges and plains. Yesterday on the 1st these were a little bigger with a weak upper cold pool with some brief afternoon showers over southern ranges and Mallee, but not quite to that level today, but nonetheless nice to look at and a reminder that we do have some moisture in the low levels ready to be utilised for the next system.
That next system is currently in the process of moving down from WA. A few days ago, a strong upper low moved north and became removed from the westerly belt and reached the northern Pilbara region of WA which is most impressive. This then proceeded to grab a large amount of tropical moisture and feed it into a broad low pressure trough causing showers, thunderstorms and areas of heavy rain. This activity is moving SE and has started to reach the far western portions of SA during today (2nd). I expect the broad trough of low pressure to slowly move SE and deepen just a little whilst being cradled by a strong high further south. This will allow the moisture to feed in from the NE also whilst meeting the moisture from the Indian and general tropics N of WA/NT.
Monday 3rd
Areas of patchy rain will extend SE and increase to reach the Eyre Peninsula by approx late morning or midday. Further it will only be patchy and largely dry anywhere south and east of Adelaide till late evening. Over the Far North and towards the top edge of the cloudband, afternoon thunderstorms should develop in the moist air and may cause local heavy falls. We should see with this style of cut off low the rain areas spreading out towards the southern end and the renewed more convective shower and isolated thunderstorms towards the N end with isolated thunderstorms.
Tuesday 4th
Areas of rain extending further south and east to reach the Upper SE District by about sunrise though the Lower SE will likely not see rain until mid-afternoon potentially and much lighter at that.
Isolated showers and thunderstorms will be ongoing in the more humid air north of the rainband, primarily over the Southern NW Pastoral to northern Eyre Peninsula and this activity will keep spreading to the rainband as it moves southward. During the afternoon with solar heating further north of the rainband, renewed surface convection should easily develop into scattered showers and thunderstorms across the Pastoral areas and adjacent agricultural districts but especially the Upper and Lower North and Riverland regions as well as the broader NE Pastoral right up towards the NT border in the broad trough of low pressure with an enhancement of NE convergence. The air will be humid here with more vigorous thunderstorm potential. Severe thunderstorms are likely over the NE Pastoral but also a possibility over the aforementioned districts with flash flooding the main threat but also potential for damaging wind and possibly large hail in the strongest cells. Showers and more isolated thunderstorms may continue to extend southwards during the evening through the Adelaide, Mt. Lofty Ranges and Mallee districts if the sustained low level NE flow can maintain convergence. Light areas of rain will remain over the Lower SE.
Wednesday 5th
The low-pressure trough will slowly begin to move southwards with the main low centre somewhere over the waters of the Bight WSW of Port Lincoln by sunrise. Isolated morning showers and thunderstorms will likely have been ongoing since midnight, chiefly over the Riverland and Mallee but also into the SE Districts. Across the border in NSW, more widespread showers and thunderstorms will thicken to areas of heavy rain as major intense broad band of rain, with embedded thunderstorms causes widespread heavy falls as mentioned earlier on. This activity will also start filtering into N VIC as all convergence focus shifts east. Consequently, Wednesday should see a reduction in activity over SA however moist to humid low levels should see isolated to possibly scattered afternoon showers develop, chiefly over the Lower and Upper North, Riverland, Mallee and the ranges but also the Eyre and Yorke Peninsula’s too. There still may be enough lingering instability for an afternoon thunderstorm about the Mallee and Riverland.
That covers the bulk of the first system however a cold front will advance from the west ahead of an upper trough reaching the Eyre Peninsula during the evening of the 6th with a band of showers and isolated thunderstorms, possibly tending to rain at times. This activity will move steadily eastwards overnight into Friday 7th, mostly clearing the eastern border by about late morning at this stage.
Further west however, an onshore westerly flow will see isolated showers continue at times although not a great deal in this before a high-pressure system gradually muscles in over the weekend of 8-9th. However, aloft things will tell a different story! An upper trough will push east above the surface high and start to tap into moist air to the NE generating areas of rain and isolated thunderstorms once again across the far N and NE portions of the state. This will then deepen a surface trough over NSW and generate yet another band of heavy rain. The trough will likely form an intense low off the NSW coast as well. If anyone is planning on heading to Bathurst for the big race, you may want to re-consider your plans as it will be a nightmare of boggy or flooded paddocks and generally a very uncomfortable event for all. The heaviest rain at this stage looks to be the night before and the morning of the big race. Another trough or low may affect the south of the state between the 10th-12th but that is subject to how the upper-level steering goes after the previous block out east that cradles all the moisture in, breaks down.
Further on, I envisage a slight respite closer to mid-month as high pressure pushes across from the west. This may open up a frost window somewhere from 14th-17th but only a low-end risk at this stage. Beyond this I think a return quite swiftly to cut off lows from upper troughs to round out the month, one potentially significant as heat enters the equation with some low to mid 30’s weather creeping south very briefly from the Pastoral zone before being replaced by the system with rain and cloud.
All in all, for the month I see nothing but above average to well above average rainfall for the entire state, not many places will miss this month. Especially however the western portions of the NW Pastoral, NE portion of the NE Pastoral will comfortably be pushing well above average. The Mallee, Upper and Lower SE should all do well. Possibly the only regions that may come closer to just average rainfall are Yorke Peninsula and KI, but I wouldn’t be surprised if we have a sea of blue on the deciles chart by the end of the month. See how we go!
Climate Drivers
The Pacific has been consistent over the last week with no huge changes either way. The Humboldt Current remains strong and the warmth over the Coral Sea with enhanced trade winds remains persistent – if anything a smidge warmer than 2 weeks ago. This warmer than average region is for mine, the biggest trump card or unknown for this spring and early summer. It certainly will provide a greater amount of tropical moisture at close proximity to the mainland with moist NE winds penetrating inland ahead of upper troughs and frontal systems. It will also be a focus for strong Tropical Cyclones and granted the lack of strong westerly shear in the area, may favour a greater chance of driving a substantial QLD coastal impact. I do envisage a system at least driving inland through QLD from the Coral Sea before turning southward and linking up with an upper trough giving significant rain to the inland portions of QLD, NSW and VIC, but especially the first two.
The Indian Is consistent as well, the Negative IOD is well established although for mine, hasn’t quite reached the expected peak in intensity just yet. It’s probably got another couple of weeks to do so before I’d say it has peaked. It is however causing impacts downstream with infeeds of moisture into N WA whilst southern WA stays dry after getting a very wet August with multiple systems. I should make note that the water directly west of PNG has warmed and is heading west so something to watch. The Western Indian remains below average.
The MJO has been quite weak of late but is slowly gathering some stead over Northern Australia. There is likely to be a small westerly pulse into the Western Pacific but that is where it probably ends. The dominance of both La Nina and the Negative IOD have taken control over the MJO to some extent holding convection over the N of the mainland and waters to the north of it. Regular thunderstorm activity has been occurring over the Western Top End for a number of weeks now with a big uptick in the last few days (mostly thanks to extra moisture pouring in ahead of this upper low over WA).
The SAM has been positive for some time now but with little dips back to near neutral at times which has allowed a reasonable balance between the tropical push from the north and the frontal push from the south but mostly due to the highs being further south, only upper-level features are meandering north with wild cut off lows aloft then inducing surface lows with lots of inland rain events and this will be a feature of October. I’ve been expecting a big multi state system in either September or October and feel later October is probably the most likely time for it once we see more heat into the centre.
Districts:
Eyre Peninsula
A broad low-pressure trough will extend from the NW with areas of rain developing on 3rd. Isolated thunderstorms also possible late evening in the far N or NW of the district. Areas of rain and isolated thunderstorms continuing 4th though rain areas contracting south early in the day with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating, chiefly in the north and east of the district. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times once more. Yet another weak front or trough due early 7th though only isolated showers at best, chiefly Lower Eyre Peninsula with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 20-30mm however grading to 35-40mm about some Lower Eyre Peninsula spots and 15-25mm more so for the Upper/Northern Eyre Peninsula.
Upper North
A broad low-pressure trough will extend from the NW with areas of rain developing during late afternoon on 3rd. Isolated thunderstorms also possible late evening in the far N near the Flinders. Areas of rain and isolated thunderstorms continuing 4th though rain areas contracting south early in the day with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating with possible severe thunderstorms. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of patchy rain at times. Yet another weak front or trough due early 7th though only isolated showers in far south about elevated peaks with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 10-20mm however grading to 20-30mm locally with possible severe thunderstorms on Tuesday afternoon. A grading down to 7-15mm more so for the Flinders portion of the district though random convective totals could still exceed 20mm there too.
A broad low-pressure trough will extend from the NW with areas of rain developing during late afternoon or early evening on 3rd. Areas of rain and isolated thunderstorms continuing 4th though rain areas contracting south by mid to late morning with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating with possible severe thunderstorms, chiefly in the north and east. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of patchy rain at times. Yet another weak front or trough due early 7th though only isolated showers or drizzle periods about elevated peaks with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 15-25mm however grading to 20-30mm locally with possible severe thunderstorms on Tuesday afternoon. A grading down to 12-15mm more so for the far west of the district.
Yorke Peninsula
A broad low-pressure trough will extend from the NW with areas of rain developing during late afternoon or early evening on 3rd. Areas of rain and possible isolated thunderstorms continuing 4th though rain areas contracting south by mid to late morning with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating, most likely in the N. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of patchy rain at times. Yet another weak front or trough due early 7th though only isolated showers, mainly about the foot with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period in N of Peninsula from 14th-17th approx. Rainfall generally 15-25mm however isolated totals to 35mm are possible about the foot. A grading down to 12-15mm more so for the far N of the district.
Kangaroo Island
A broad low-pressure trough will extend from the NW with areas of patchy rain developing by early morning on 4th before tending to broader areas of rain through the morning though rain areas contracting south by mid to late afternoon with humid conditions becoming established. Possible evening shower or thunderstorm lingering. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times. Yet another weak front or trough due early 7th though only isolated showers with a final trough or low possible from 10th-12th with shower activity. Frost risk very slight right at end of period in centre of island from 14th-17th approx. Rainfall generally 18-25mm however isolated totals to
30mm are possible about the western end. A grading down to 15-18mm more so for the far E of the island.
Adelaide Plains
A broad low-pressure trough will extend from the NW with areas of rain developing during late evening on 3rd. Areas of rain and possible isolated thunderstorms continuing 4th though rain areas contracting south by mid to late morning with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating, most likely in the N about the outer plains and northern foothills although activity may extend further south during the evening. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times. Yet another weak front or trough due early 7th though only isolated showers, mainly about the foot with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period over outer plains from 14th-17th approx. Rainfall generally 20-30mm however isolated totals to 35mm are possible closer to foothills and in the southern suburbs or under any thunderstorm activity further N. A grading down to 15-20mm more so for the western suburbs.
Mt.Lofty Ranges
A broad low-pressure trough will extend from the NW with areas of rain developing during late evening on 3rd. Areas of rain and possible isolated thunderstorms continuing 4th though rain areas contracting south by mid to late morning with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating, most likely about northern ranges before activity may extend over remaining portions of the ranges in evening although quite isolated. Further afternoon showers on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times. Yet another weak front or trough due early 7th though only isolated showers, mainly about the foot with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period over low lying valleys from 14th-17th approx. Rainfall generally 25-40mm however isolated totals to 50mm are possible closer to higher peaks and known wet spots or under any thunderstorm activity further N. A grading down to 20-25mm more so for the far N ranges closer to the plains and also eastern slopes.
Riverland/Mallee
A broad low-pressure trough will extend from the NW with areas of rain developing early during 4th and increasing during the morning before contracting south early in the afternoon with humid conditions becoming established. Renewed isolated afternoon showers and thunderstorms developing with surface heating with possible severe thunderstorms over the Riverland. Showers and isolated thunderstorms continuing to extend south during the evening. Further afternoon showers and a possible thunderstorm on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th or early 7th with band of showers and possible isolated thunderstorms and this may tend to areas of patchy rain at times. Yet another weak front or trough due early afternoon 7th though this probably gets washed out over the ranges with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 15-25mm however grading to 20-30mm locally with possible severe thunderstorms on Tuesday afternoon. A grading down to 10-15mm more so for the western Riverland and Mallee though random convective totals could still exceed 20mm there too.
Upper SE
A broad low-pressure trough will extend from the NW with areas of rain developing early during 4th and increasing during the morning and early afternoon before contracting south later in the afternoon with humid conditions becoming established. Late afternoon showers and isolated thunderstorms will begin to extend south behind the rainband. Showers and isolated thunderstorms continuing to extend south during the evening and into early hours of 5th. Further afternoon showers and a possible thunderstorm in the N on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th or early 7th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times. Yet another weak front or trough due early afternoon 7th with isolated light showers with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 20-30mm however grading to 40mm locally in parts. A grading down to 18-20mm more so for Coorong coastline but mostly a consistent drop of rain for the period.
Lower SE
A broad low-pressure trough will extend from the NW with areas of rain developing early during 4th and increasing during the morning and early afternoon before contracting south later in the evening with humid conditions becoming established. Showers and isolated thunderstorms continuing to extend south during the evening and into early hours of 5th. Further afternoon showers in the N on 5th but as trough moves further south, convergence and lift will decrease. Cold front then extending from west later on 6th or early 7th with band of showers and possible isolated thunderstorms and this may tend to areas of rain at times. Yet another weak front or trough due early afternoon 7th with
isolated light showers with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 20-30mm however grading to 35mm locally in parts with no totals under about 20mm district wide.
Western VIC
A broad low-pressure trough will extend from the NW with areas of rain developing over the Mallee District early during 4th and increasing during the morning and early afternoon before contracting south later in the afternoon with humid conditions becoming established. Late afternoon showers and isolated thunderstorms will begin to extend south behind the rainband with severe thunderstorms possible over the Mallee and possibly also the Wimmera. Showers and isolated thunderstorms, tending to rain areas continuing to extend south during the evening and into early hours of 5th with local heavy falls developing further east. Activity easing through the daylight hours to patchy rain but still a possibility of an afternoon thunderstorm but as trough moves further south, convergence and lift will decrease slowly. Ahead of a cold front on 6th, more showers will develop during the afternoon with solar heating and also the possibility of another afternoon thunderstorm. The cold front then extending from west early 7th with band of showers and possible isolated thunderstorms, and this may tend to areas of rain at times. Yet another weak front or trough due early afternoon 7th with isolated light showers with a final trough or low possible from 10th-12th with shower activity. Frost risk slight right at end of period from 14th-17th approx. Rainfall generally 25-40mm however grading to 50-70mm towards the far east/NE. A grading down to 20-25mm more so towards the SA border.
Finals Notes:
- Major rainfall and flooding to occur over much of NSW but also parts of N/NE VIC and S QLD.
- Potential for Murray levels to reach 1973-1975 type levels though may come shy on 1974.
- Flooding will occur through SA along the Murray as slow onset flooding with the huge flows from upstream rains
- La Nina and negative IOD having maximum combined effect in October before Indian influence waves.
- Coral Sea influence will increase as we warm peaking in December to January
- Becoming hotter and drier through Jan-Feb for SA however a slight easing may be observed in December too. Not so for eastern states.
- Special updates will be issued for any new significant events
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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