November outlook 2024 SA

 November outlook 2024 SA

  

*Forecast prepared between October 29th-Nov 3rd 2024  

  

Review:  

G’Day everyone, I trust and hope that you are all keeping well. Time for the November update – I did consider an October mid-monther but due to personal commitments and a lack of significant rain/weather systems, I decided to abandon that. The main talking point to review is indeed that thunderstorm system that we had on the 17^th which was in our broader instability window first hinted in the initial October outlook. It was nice for it to come together for a change but no doubt with very mixed feelings for many. Too late for probably 90% of crops but useful for tanks and dams but no good for those cutting hay.

The lead up to the event saw some ‘pre-wetting’ of the surface across primarily the Lower and Upper North (and a little into the Riverland and Mallee) with some areas of rain and isolated thunderstorms. The moisture feeding in from the tropics was the most significant since the previous summer. Aloft a sharpening upper trough was approaching whilst at the surface a strong cold front intersected a deepening low which enhanced convergence in the low levels whilst the upper trough and jetstream enhanced divergence in the upper levels. This essentially worked as a well-oiled machine. Showers and thunderstorms developed early across the Eyre Peninsula before peak surface heating occurred. A warm front advanced south in the wake of the earlier activity allowing a warm to hot and humid warm sector to prevail ahead of the cold front. Thunderstorms rapidly developed across the Eyre Peninsula and NW Pastoral zones before heading SE. Severe left and right moving supercells also developed with a right mover shooting past Whyalla into the Kapunda area and a very destructive left mover hooked into the southern portions of Port Pirie and adjacent areas. The frontal line then came in behind whilst a lot of the thunderstorm activity began to clutter and turn into heavy rain areas with good falls in the order of 30-60mm right across the Lower and Upper North and 20-40mm across a lot of the Riverland and much of the Mallee. Falls did taper off quite a bit south of there. I only received 2mm in southern Adelaide which was a big miss and a mere 3.4mm for the month.

I also should make a mention that I did head up to the Upper North area to intercept the storms and used it as an opportunity to take a look at the state of the land and to be honest it was truly shocking in some areas that I drove by. One area south of Spalding was quite bad for such a good rainfall part of the general Mid North but the landscape between Jamestown and especially a little south of Orroroo was truly awful and was a good fit for Mars. It is very clear how dry the area is and has been for a long time now – the drought there was intense.

Now taking a look back at the month in terms of charts, we see the following:

Figure 1: October 2024 rainfall deciles – source BoM http://www.bom.gov.au/climate/

Figure 2: October 2024 rainfall percentages– source BoM http://www.bom.gov.au/climate/

 

Figure 3: October 2024 rainfall anomalies– source BoM http://www.bom.gov.au/climate/

Now it is clear that there was a wide variance in rainfall statewide during October, with the bulk of all rainfall coming from one single even on October 17^th, which as mentioned just above, primarily cut a swath through the Lower and Upper North as well as the Riverland and Mallee. After this, there hasn’t been much apart from some isolated showers.

The percentages chart shows the greatest detail as always and we can see some above average areas from this single system through far northern Yorke Peninsula, general Lower and Upper North (moreso eastern parts and the Flinders, pushing into the Southern NE Pastoral and Riverland.

The driest areas clearly were around the Adelaide and Mount Lofty Ranges with no frontal systems of any note which usually still deliver some orographically enhanced rainfall to the region. Central to southern Yorke Peninsula also came in below average as did the Lower SE and a swath of the Eyre Peninsula northwards to the Pastoral zones. The best rainfall was confined to the far western border near WA. Overall, better than September but still more average to below average rainfall with smaller areas of above average.

Looking back at the forecast we had the following:

“Overall, my outlook for October is for average to slight below average rainfall across most agricultural districts. The greatest chance of average rainfall or slightly above again is the Lower SE which like September will just be south enough to receive fronts. The greatest chance of above average again will be the western border areas up to about Western Eyre Peninsula but moreso into the NW corner of the state”

The first thing that stands out is the miss in the Lower SE – the fronts simply did not even get that far north so you know it was bad. Everywhere else performed closer to expectations although nailing the specific thunderstorm area through the Mid North was a little beyond the precision of general outlooks. The trend to the far west worked at least. Large other areas were average to below average.

Meteorological Discussion:

November is now here and a month where no doubt many of you are busy out in the field hopefully harvesting something at least but I understand that may not be the case for a number of you this year. The rainfall in October for the areas it did hit, was in some cases most welcome but in others not so welcome so quite a mixed bag. But now in November that window for useful rainfall has essentially ended for this season’s benefits although at least deep moisture now would help into 2025.

The current patterns sees a fast and mobile zonal flow with troughs and weak fronts every few days and rapidly fluctuating temperatures however these are nothing extreme for this time of the year – we have had far more intense heat in October and November that we are getting right now and the zonal pattern is allowing this. Zonal flow is where we have more dominant westerlies and rapid moving systems as opposed to meridional flow which is prone to blocks allowing heat to build over the interior without being removed by cool changes and that usually builds all the way down into our state, assisted by more high amplitude fronts and deeper upper ridging promoting a classic heatwave pattern. Right now, we do not have that which is one thing to be thankful for. Nevertheless, still expect a number of hot days ahead of these fast-moving troughs and cold fronts.

The first point of interest will be a weak but fast-moving trough of low pressure on the 5^th which is expected to generate showers and thunderstorms, chiefly across areas north of about Kangaroo Island and these should weaken mostly east of the Mt.Lofty and Flinders Ranges as the trough starts to wash out. Initially we should see morning isolated mid-level showers and thunderstorms, increasing and speading eastwards to general showers and thunderstorms, with a focus across the Eyre Peninsula, NW Pastoral, Yorke Peninsula, Upper North and Lower North with a slightly weaker focus for the Central areas of the Adelaide Plains and Mt.Lofty Ranges although there still should be enough activity around. These will be mid-level/high based with the primary risk being lightning starting fires as rainfall activity will be low. Damaging winds are the other likely feature for the stronger thunderstorms that are likely to develop during the afternoon across the Eyre Peninsula (chiefly the northern half) most of the NW Pastoral, Flinders and possibly some of Lower and Upper North/Northern Yorke Peninsula. Essentially the risk of severity decreases with southern and eastern extent. I should also make note that there is a chance of large hail (up to 3cm or so) in the strongest cores, most likely over the Pastorals and Eyre Peninsula but potentially also extending just east of the gulf areas.

Beyond this event we should continue to see a fluid pattern with a couple of cold fronts due in with some shower activity over chiefly the southern coastal districts. The first is due early on the 7^th with a band of showers generally. There will be some colder air aloft immediately behind this one and with the timing, isolated thunderstorms are likely to develop over the east of the ranges and across the Mallee, Upper and Lower SE. The second, likely a tad weaker and further south is due on the morning of the 8^th with a further broken band of showers but not a lot in it. Given the upper-level flow aloft will still be from the NW and relatively cool, some showers could be locally heavy on the 7^th system about the southern Fleurieu and adjacent coastal districts including Kangaroo Island.

Further north isolated showers and thunderstorms are likely to re-develop in a broad jetstream induced flow and surface trough ahead of the 7^th front further south.

After this all clears a weak high-pressure system will move through the Bight with mostly fine and mild to warm conditions across most agricultural districts. A deepening trough is likely towards the NW of the state from about the 9^th with isolated showers and thunderstorms in the NW corner and adjacent Far North areas. High pressure ridging and zonal flow should keep most of this activity well north however as we approach mid-month, I expect the shower and thunderstorm activity to become more persistent on a daily basis over the interior as a broad trough deepens across the state. Moisture looks to feed into this system well however I do expect more substantial and longer lived tropical infeeds by the end of the month as the zonal flow relaxes.

My overall November outlook is for average rainfall, tending to above average with northern and especially NW extent. Towards the SE Districts there is an increased risk of below average rainfall. Most of the above average chances will be attributed to thunderstorms over mostly the second half of the month. Locally above average totals are possible over agricultural areas, chiefly over the Eyre Peninsula and Upper North.

Climate Drivers:  

The Pacific remains in a cool neutral state, ever so slowly trickling to a weak La Nina. It is close but it’s not there yet despite the fact the Nino 3.4 index has been hovering near –1 for almost the entire month. Another month in this territory and it will be declared by NOAA. The BoM however I don’t expect to call it as they are always more conservative but nevertheless it is right on the edge now for the expected peak in December as usual.

 

Figure 4: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png

Now the real talking point is the Indian, with a complete flip to a moderate strength Negative IOD (expected but the magnitude has even surprised me) with the latest reading being –0.94C, the lowest since 2022. Never in history have we had a value like this in October but be faced with such incredible dryness. The flip flopping of the index all year has not helped patterns establish but this final late dive will certainly assist in November and December moisture infeeds primarily from thunderstorm activity. We have already seen one big intrusion as mentioned on the 17^th of October. I expect similar systems more so through mid to late November and December. Right now, the pattern is quite mobile and the tropics resetting the moisture levels so it will not be captured. The index will have a real crack at becoming official, it’s going to be a close call for the time frame needed but I think it just gets there (7 consecutive weeks under –0.4C). Figure 4 above shows the cooler area off Africa well and the warmer water off Indonesia. Not long ago it was colder off Indonesia. The entire Indian right now apart from that Western IOD box is above average in temperature.

Moving on to the SAM, and we have seen a relatively neutral phase of late but with a slight negative flavour at times with a mobile pattern of fast-moving fronts and troughs. Alas, these have been weak and merely wind changes or some isolated thundery showers at best. The upper-level pattern is a little conducive to increased thundery signatures on most changes at the moment, so a little more strength in the systems will allow for that activity. You may have at least noted a lot of Altocumulus Castellanus in the skies near the changes which is one of the signs I look for in spring and early summer especially. But until the SAM goes a little more positive, the moisture will struggle to feed in with much gusto. I expect the second half of November and into December to see that improvement.

The MJO has made a fairly decent move into the Pacific and is now entering phase 8 on the other side of the world at quite a strong amplitude. This has been the strongest pulse of the spring and will go towards slowing any further significant La Nina development. Hence what we see now is very close to what we will get in that regard as per the Pacific section. The next pulse the one of most interest and that is due mid to late November when the westerly belt should begin to ease a little allowing more easterlies ahead of the fairly solid MJO pulse. The pulse will gradually weaken as it moves over the Australian mainland area through later November, but no doubt will increase moisture and thunderstorm activity across much of the continent.

Districts:    

Eyre Peninsula  

Trough on 5^th bringing increasing showers and thunderstorms. Isolated severe thunderstorms possible during the afternoon, chiefly towards the northern half of the Peninsula before clearing eastwards during the evening. Weak fronts crossing chiefly the Lower Eyre Peninsula on the morning of the 7^th and 8^th with isolated to scattered showers. Remaining generally dry north of here. New ridge moving in from Bight clearing shower activity although showers and isolated thunderstorms may develop in the far west of the district later on the 9^th potentially as influence from a deepening trough over the NW interior begins to take hold. This activity may linger into the 10^th before clearing ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 4-8mm generally with isolated 15mm falls possible. Very local 20mm totals may occur in one or multiple thunderstorms towards the north of the Peninsula.

Upper North  

Trough on 5^th bringing increasing showers and thunderstorms. Isolated severe thunderstorms possible during the afternoon, chiefly towards the Iron Triangle and Flinders before clearing eastwards during the mid to late evening. Weak fronts crossing over the south of the district on the morning of the 7^th and 8^th with some isolated showers in the south. Remaining generally dry north and east, however. New ridge moving in from Bight clearing shower activity although showers and isolated thunderstorms may develop from the west or NW of the district later on the 9^th potentially as influence from a deepening trough over the NW interior begins to take hold. This activity may linger into the 10^th before clearing ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 4-10mm generally with isolated 15-20mm falls possible. Very local 25mm totals may occur in one or multiple thunderstorms towards the Iron Triangle and Flinders.

Lower North  

Trough on 5^th bringing increasing showers and thunderstorms. Isolated severe thunderstorms possible during the afternoon, chiefly towards the Spencer Gulf Coastline and Upper North border before clearing eastwards during the mid to late evening. Weak fronts crossing over the south of the district on the morning of the 7^th and 8^th with some isolated showers, chiefly in the south. Remaining generally dry north and east, however. New ridge moving in from Bight clearing shower activity although showers and isolated thunderstorms may develop from the west or NW of the district later on the 9^th potentially as influence from a deepening trough over the NW interior begins to take hold. This activity may linger into the 10^th before clearing ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 3-8mm generally with isolated 10-15mm falls possible. Very local 18mm totals may occur in one or multiple thunderstorms towards the Spencer Coast and Upper North Border.

Yorke Peninsula  

Trough on 5^th bringing increasing showers and thunderstorms. Isolated severe thunderstorms possible during the afternoon, chiefly towards the far north of the Peninsula before clearing eastwards during the evening. Weak fronts crossing chiefly the lower half of the Peninsula on the morning of the 7^th and 8^th with isolated to scattered showers along the frontal band. Showers much more isolated over the northern half. New ridge moving in from Bight clearing shower activity although showers and isolated thunderstorms may develop in the far north of the Peninsula later on the 9^th potentially as influence from a deepening trough over the NW interior begins to take hold. This activity may linger into the 10^th before clearing ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 2-6mm generally with isolated 10-12mm falls possible. Very local 15mm totals may occur in one or multiple thunderstorms towards the north of the Peninsula.

Kangaroo Island  

Trough on 5^th bringing isolated showers and thunderstorms before clearing eastwards during the evening. Weak fronts on the morning of the 7^th and 8^th with scattered showers along the frontal band, especially on the 7^th. New ridge moving in from Bight clearing shower activity. Another trough due around mid-month with showers and thunderstorm activity. Rainfall for the period 2-6mm generally with isolated 10-12mm falls possible from the fronts.

Adelaide Plains  

Trough on 5^th bringing increasing showers and isolated thunderstorms before clearing eastwards during the evening. Weak fronts on the morning of the 7^th and 8^th with isolated to scattered showers along the frontal band. Showers much more isolated over the outer northern plains. Locally heavy showers possible about foothills on 7^th. New ridge moving in from Bight clearing shower activity thereafter ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 4-6mm generally with isolated 10-12mm falls possible about the foothills.

Mt.Lofty Ranges 

Trough on 5^th bringing increasing showers and isolated thunderstorms before clearing eastwards during the evening. Weak fronts on the morning of the 7^th and 8^th with isolated to scattered showers along the frontal band. Showers much more isolated over the outer northern plains. Locally heavy showers with isolated thunderstorms possible on 7th, chiefly off the backside of the ranges. New ridge moving in from Bight clearing shower activity thereafter ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 5-10mm generally with isolated 10-15mm falls possible about the higher peaks and rear of the ranges (localised).

Riverland/Mallee  

Trough on 5^th bringing isolated showers and thunderstorms, chiefly afternoon and evening before clearing eastwards during the later evening. Weak fronts on the morning of the 7^th and 8^th with isolated to scattered showers along the frontal band. Isolated afternoon thunderstorms over the Mallee on the 7^th on and ahead of the frontal band. Showers much more isolated over the Riverland. Possible mid-level showers and isolated thunderstorms on later 9^th and into 10th about the Riverland. New ridge moving in from Bight clearing shower activity thereafter ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 2-4mm generally over the Mallee with isolated 10-12mm falls possible from thunderstorms. Totals decreasing to 1-2mm over the Riverland.

Upper SE  

Trough on 5^th bringing isolated showers and thunderstorms, chiefly afternoon and evening before clearing eastwards during the later evening. Weak fronts on the morning of the 7^th and 8^th with isolated to scattered showers along the frontal band. Isolated afternoon thunderstorms possible on the 7^th on and ahead of the frontal band. New ridge moving in from Bight clearing shower activity thereafter ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 3-5mm generally with isolated 10-12mm falls possible from thunderstorms.

Lower SE  

Trough on 5^th bringing isolated showers and thunderstorms, chiefly afternoon and evening and more likely closer to the Upper SE border before clearing eastwards during the later evening. Weak fronts on the morning of the 7^th and 8^th with scattered showers along the frontal band. Isolated afternoon thunderstorms possible on the 7^th on and ahead of the frontal band. New ridge moving in from Bight clearing shower activity thereafter ahead of another trough due around mid-month with similar shower and thunderstorm activity. Rainfall for the period 4-8mm generally with isolated 10-12mm falls possible from thunderstorms.

Western VIC  

Trough late on 5th and early 6^th bringing isolated showers and thunderstorms although weakening as they cross from SA. Weak fronts on the morning of the 7^th and 8^th with scattered showers along the frontal band. Isolated afternoon thunderstorms possible on the 7^th on and ahead of the frontal band. New ridge moving in from Bight clearing shower activity thereafter. Slight chance of some mid-level showers and isolated thunderstorms on the 11^th with a weak trough over the Mallee chiefly. Another trough due around mid-month with similar shower and thunderstorm activity.  Rainfall for the period 4-8mm generally with isolated 10-12mm falls possible from thunderstorms.

Final Notes  

·         Showers and thunderstorms on 5^th with trough, some possibly severe over Western and Northern SA. A high fire risk is likely from high based Cloud to Ground (CG) lightning

·         Fluid pattern with multiple troughs embedded under a broad W to NW flow aloft

·         Moisture building over tropics for later November where increased rainfall from showers and thunderstorms is likely

·         Negative IOD should become official later in November

·         La Nina unlikely to become official but more of a cool neutral

 

  

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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.