June Outlook 2024 SA

June Outlook 2024 SA

*Forecast prepared between June 2nd-4th 2024

Review:

G’Day everyone, winter is here! And certainly, off to a cold start with some frosty mornings right across the state, including KI where Kingscote Airport has recorded –0.2C and –0.9C for the first two mornings of the month which is very cold for that part of the world. Keith recorded –1.8C on the 2nd and at the time of typing this, it looks like the morning of the 3rd will be the coldest with potentially some moderate frost and –2C minimums at least in some prone locations such as the Clare Valley and Riverland. I hope the warning in the most recent quick update was of use for these sudden frosts although not a huge deal can be done about them.

Reviewing further back in May and we can safely say it was a shocker of a month, right up until the last couple of days at least when finally, a decent NW cloudband and cold front with cold air moved through. A secondary little shortwave then kicked in on the 31st to keep totals ticking over but not for all. Without this system, the month would have set countless dry records across the state. Let's take a quick look at the rainfall maps below to see how the distributions were across the state.

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

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

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

Now overall, we can certainly see it was a poor month, even with the rain right at the end, there were still a few pockets of lowest on record. That area of red would have vastly greater if not for that late system, but the lighter red still dominates. The NE corner was the fortunate area getting some handy rainfall from the NW cloudband as well as a little bit earlier in the month. Looking back at the May outlook below, we can see how things performed:

"Overall, for May, my forecast is for a below average month for most districts as I had targeted it for around average to potentially even above average. Nevertheless, the far NE Pastoral will see the best chance of above average rainfall due to the trough and weak upper low. Most other districts will be below average to well below average rainfall as patchy and sliding frontal systems make up that moisture. I will be able to give more clarity whether or not the longwave trough will make a dent in our region by the end of May in the mid-month update which also will be critical."

Broadly the final outlook proved to play out roughly as expected but to be honest it was drier overall than I thought, even after making that amendment given a few months ago, May was the period I had pencilled in for a change in the pattern. The block had other ideas and was criminally underestimated. A lesson learnt to take forward, but it certainly was one of the most persistent and long-lived dry patterns we have seen in the last 30 years.

Meteorological Discussion:

Currently we are in the wake of our first rains of the season – a patchy break if you want to call it that. Some locations would be calling it a breaking rain, but many will not with some meagre rainfall totals that simply haven’t cut the mustard yet and this all comes back to that drawn out and frustrating break mentioned in previous outlooks.

The block has begun to breakdown down and let fronts with moisture in, however despite what we saw the other day, the main Longwave Trough is stuck just west of WA which is fantastic for them, and much needed. A little drier in parts of the Great Southern and SE coastal where shadowing is present, but the SW especially has been and will continue to be in the firing line for multiple strong cold fronts for most of June before this Longwave decides to shift eastwards through the second half of the month. I would go as far as saying that June 2024 will be one of the wettest on record for SW WA, on the ranges and SW/W of. This certainly is needed due to the decline in groundwater levels in the last 50 years. Farmers inland across the Wheatbelt should see a big relief by the end of June with the Indian Ocean being a significant source of tropical moisture feeding into those fronts rotating around the longwave trough.

But on to the current proceedings and we have a developing upper low which is pinching off from the westerly belt over SA. This is happening due to the blocking ECL that has formed off NSW in the Tasman thanks to that last little shortwave from May 31st. I did mention that it will hinder things and whilst some light patchy rain is falling across the NW Pastoral and most locations west of the ranges, minimal totals have been recorded with only Ceduna really getting anything significant with 9.8mm to 9am. Other parts of the West Coast and northern Eyre Peninsula saw 4-8mm totals which would have been useful at least but further east of the Spencer Gulf, most totals were 1mm or less. At least evaporation levels won’t be too high.

With this system weakening and moving east, the upper low will push into NSW from inland SA over the coming day or two and will once again interact with the moisture coming in off the Tasman Sea and generate, you guessed it, another ECL. Fortunately, this one won’t block another good system coming from the west, but it will cause a high to anchor over the state for as few days which will bring back the frost risk to a similar level that we saw over the last few mornings. The main risk window is the 5th to the 8th inclusive, but especially the 5th followed by the 7th mornings where a slight to moderate risk is present, the other mornings it should be more on the slighter end than moderate. I can also see another risk period around the 14th-16th after the colder air from fronts beforehand. There could be some slight drizzly streams in the southerly flow on the 5th ahead of the next large high pressure, but these will vanish on sundown as the rapid cooling occurs at the surface.

After this ridge moves east it will weaken allowing a weak front to extend from the west across primarily the southern agricultural areas on approximately the 8th with some scattered showers and a little bit of cold air stream shower activity behind it, but with poor inland penetration – it will be quite a west to east type of weak front.

Another weaker high-pressure ridge will follow this but will follow the trend of weakening zones of high pressure from what we were used to seeing through much of autumn and especially May. A warm front is then likely on the 10th as we see another push aloft from the NW as the flow gets squeezed by the longwave trough to the west. A large low-pressure system with embedded fronts is then likely to move eastwards off this longwave trough in the 11th-13th period with one or two cold fronts crossing the state, chiefly the southern portions. A pool of cold air follows but the trajectory at this stage still looks too west to east to get good inland penetration. Rain shadow will again be significant for the Riverland and northern Mallee with the southern portions at least doing ok however the front will weaken as it moves eastwards. We still need the longwave to shift east with the much colder air to drive that flow inland and that is more likely in the second half of the month than the current phase. There is a chance of a squeezed jetstream in this NW-SE regime given some mid-level rain areas at times as well so will keep an eye on this but if the low sags south anymore, that won’t happen.

Now below are two charts showing exactly what I mean by the ‘Longwave Trough’. You have probably read it many times lately but to picture it, essentially what we have is a broad area of low pressure analysed in the mid-levels and the best level to do that is the 500hPa level which is roughly averaged out to about 18,500ft but due to extreme warm or cold atmospheres, that can change. So, in Figures 4 and 5 the Longwave Trough is the arch shaped purple area sitting SW of WA rising up out of the westerly belt that wraps around the South Pole. Note the areas ahead of it have persistent NW flow and this is where the jetstream is often stronger with the jetstreak or speed max occurring on or just ahead of the apex of this large-scale upper trough. If we analysed it a t the surface we would see a broad area of low pressure with multiple lows, shortwave troughs and fronts embedded within it, all rotating up and down the main area. Some of these can pinch off or cut off which is what we see over SA in Figure 4. The main take home message though from Figure 4 and Figure 5 is for the most part, the Longwave Trough is stuck to the SW of WA. This explains why so many strong cold fronts have been easily able to clobber the SW of WA but then struggle further east. Once this whole area shifts east then it will allow our fronts to be more frequent and stronger.

Having said that, I wouldn’t expect the strength we see here, perhaps a slightly weaker version given how strong it currently is.

Figure 4: ECMWF AIFS model forecast for the 500hPa(`18,500ft) level on 04/06/24 @ 1530ACST

Figure 5: ECMWF AIFS model forecast for the 500hPa(`18,500ft) level on 19/06/24 @ 0330ACST

Now as far as the rest of the month goes as a whole, my official outlook is for very close to average rainfall for areas west of the ranges but slightly on the lower side of average. The West Coast and Eyre Peninsula have the greatest chance of getting above average rainfall as well as parts of the NW Pastoral District. Whilst I see a good increase in fronts and rainfall this month, the fractured nature of the break combined with the fact that June is usually the wettest month of the year means that we will be working quite hard to exceed averages everywhere. The greatest chance of below average rain will be immediately east of the ranges, across the Upper North and generally the SE Districts and Kangaroo Island. The latter whilst getting more rain than most districts, normally gets battered by winter fronts and has quite a high average rainfall for June. Having said that, it shouldn’t be too much below. Most other areas should be closer to their average but slightly below. So, in short, yes a much better month but we expect this and despite the improvement, I still see things falling just short for the majority.

Climate Drivers:

It is no surprise now that we are on a La Nina watch which has been issued by the BoM. We have been moving towards this for quite some time and the setup has been obvious with all the tell-tale signs from the Humboldt Current starting to flow and upwell that cold water off the west coast of South America to the surfacing cold pool from the Nino 3.4 region and east of which has been evident on the SST anomaly charts. The latest image of that can be seen below in Figure 6:

Figure 6: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png

The colder tongue whilst perhaps a little bit less than 2 weeks ago, remains fairly persistent. Trade winds are about average however in recent weeks due to the block have been very persistent into the east coast of Australia and these winds have been moistened by the warmer SST’s off the east coast of Australia – it is no surprise why it has been so wet there. A striking part of the image above is the extremely warm Northern Pacific, and it is thought that this area has been a big player in the above average to near record tornado season in the USA this year. Further west towards our part of the world, most of the waters to our north and NE remain above average with only very small pockets of below average. The fuel is there and this development phase of the impending La Nina will continue.

Now onto the all-important Indian and we have seen some solid movement in the Western IOD box area off the Horn of Africa with the waters beginning to cool in the last 7 days. Now this is likely to only be temporary, but it will certainly dent the formation of a Positive IOD – something I have been calling false for some time now despite modelling being overwhelmingly in favour of. There will be another attempt at this in July, but I think it all gets stopped out from developing. The recent eastward shift in the block has allowed moisture to feed SE into Australia as well as increase the convection across the Central and Eastern Indian, right into Indonesia which is a good sign. It also helps reduce the upwelling from strong trade winds now that the never-ending highs have begun to reduce in their intensity and frequency. I still expect an attempt at a Negative IOD as we move into Spring, it’s going to be very hard for cold water to dominate anywhere in the Indian basin as it should remain above average as a whole. This combined with the developing La Nina should help increase the spring rainfall especially.

The SAM has been slightly negative in recent days after a long and sustained positive phase through May which was a result of high-pressure systems dominating and sitting well south causing the polar vortex to contract. This index should fluctuate between negative and neutral through most of June with only brief positive bursts. As the longwave trough shift eastwards after roughly the 12th of June, we should see this index push back to lower values. The latter part of the month sees the greatest chance of colder air from deeper SW-S flow with the Longwave Trough to our east.

The MJO is currently in phase 6 after moving across the mainland over the last 2 weeks at a moderate strength. It was stronger in the Eastern Indian and did assist in providing some moisture from increase convection. All signs point towards another pulse in our window around early to mid-July at a moderate strength again. If this keeps up, the westerly bursts across the Eastern Indian will help thwart any cold water upwelling and thus weaken off a Positive IOD that may be trying to form. I have July marked as a drier month with more frontal influence only and less big infeeds. The MJO generally doesn’t help much in mid-winter when ‘normal’ patterns are present however if lingering convection across Indonesia remains, then the influence whilst minimal, will be enough to have some impact on what feeds into our country.

Districts:

Eyre Peninsula

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light coastal showers on Spencer Gulf coast on 5th. Cold nights from 5th to 8th with slight frost risk, especially on 5th and 7th. Weak front on 8th with isolated showers, chiefly over Lower Eyre Peninsula. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail about Lower Eyre Peninsula in colder air behind the front with more frequent and heavier shower activity. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk. Rainfall for the period till 15th generally 5-8mm, increasing to 10-15mm about Lower Eyre Peninsula. Totals decreasing markedly towards the N/NE of the Peninsula down to around 2-5mm.

Upper North

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light drizzly showers possible near higher terrain. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th. Weak front on 8th with isolated showers, chiefly in the far south only. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Showers will be isolated north of about Port Pirie to Jamestown. Possible small hail in the far south in colder air behind the front. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially in the N and E of the district. Rainfall for the period till 15th generally 3-6mm, increasing to 6-10mm about higher terrain. Totals decreasing markedly towards the back side of the ranges and north of about Port Augusta down to around 1-3mm.

Lower North

Upper low causing patchy light rain clearing later on 4th and mostly in the north. Ridge moving in behind with initial southerly flow with light drizzly showers possible near higher terrain, chiefly southward facing slopes. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th. Weak front on 8th with isolated showers, possibly scattered briefly in the far south. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail in colder air behind the front. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially in the N and E of the district. Rainfall for the period till 15th generally 4-8mm, increasing to 7-12mm about higher terrain. Totals decreasing markedly towards the back side of the ranges down to around 1-4mm.

Yorke Peninsula

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light showers possible on 5th. Cold nights from 5th to 8th with a slight frost risk, especially on 5th and 7th and moreso over the northern portion of the Peninsula. Weak front on 8th with isolated showers, chiefly over the foot of the Peninsula. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail about in colder air behind the front with more frequent and heavier shower activity near the foot. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially in the north. Rainfall for the period till 15th generally 5-10mm, increasing to 10-15mm about the foot of the Peninsula. Totals decreasing towards the N of the Peninsula down to around 4-5mm

Kangaroo Island

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light showers possible on 5th. Cold nights from 5th to 8th with a slight frost risk, especially on 5th and 7th chiefly near the centre of the island. Weak front on 8th with isolated to scattered showers, clearing later. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail and isolated cold air thunder in colder air behind the front with more frequent and heavier shower activity. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially in the island centre once again. Rainfall for the period till 15th generally 12-17mm, increasing to 20mm about the western end. Totals decreasing towards the E of the island down to around 10-12mm.

Adelaide Plains

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light showers possible on 5th, chiefly about the southern suburbs. Cold nights from 5th to 8th with a slight frost risk, especially on 5th and 7th and moreso over the outer plains. Weak front on 8th with isolated showers, chiefly south of about Gawler and tending scattered over the southern suburbs. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail about in colder air behind the front with more frequent and heavier shower activity south of about Gawler. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially about the outer plains. Rainfall for the period till 15th generally 5-12mm, increasing to 12-15mm near the foothills. Totals decreasing towards the coastal strip and suburbs down to around 5-6mm.

Mt.Lofty Ranges

Upper low causing patchy light rain clearing later on 4th. Ridge moving in behind with initial southerly flow with light showers on 5th, chiefly about the southern coasts and ranges and running up the backside of the ranges in small streams. Cold nights from 5th to 8th with a slight frost risk, especially on 5th and 7th and moreso in low lying valleys and the Barossa where the risk is closer to moderate. Weak front on 8th with isolated showers, scattered towards the southern ranges. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail about in colder air behind the front with more frequent and heavier shower activity south of about the Barossa. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk, especially about the Barossa. Rainfall for the period till 15th generally 15-20mm, increasing to 25-30mm near known wet spots and higher terrain. Totals decreasing towards the Barossa down to around 5-10mm and also the backside of the ranges where even less down to 4-5mm is likely.

Riverland/Mallee

Upper low causing very light patchy rain clearing later on 4th. Ridge moving in behind with initial southerly flow with a possible light shower in the SW of the Mallee. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th. Weak front on 8th with isolated showers, chiefly in the far south only. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Showers will be more isolated over the Riverland and northern Mallee. Possible small hail in the far south of the Mallee in colder air behind the front. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk across both districts to a moderate level. Rainfall for the period till 15th generally 3-5mm about the Southern Mallee with isolated falls to 7mm possible in the far south. Totals decreasing to 1-3mm in the north and Riverland with some areas receiving less to almost immeasurable rainfall in the northern Riverland.

Upper SE

Upper low causing very patchy light rain in the north, clearing later on 4th. Ridge moving in behind with initial southerly flow with some possible light showers, mainly near the Coorong coast and towards the Lakes. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th. Weak front on 8th with isolated showers, tending scattered in the south. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Possible small hail in colder air behind the front with more frequent and heavier shower activity closer to the Coorong coastline where isolated cold air thunder is also possible. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk significantly with a moderate risk likely. Rainfall for the period till 15th generally 8-12mm, increasing to 15mm in the far south and SW. Totals decreasing towards the Mallee down to around 6-8mm.

Lower SE

Upper low with mid-level cloud but largely remaining dry on 4th. Ridge moving in behind with initial southerly flow with some possible light showers, mainly near the coast. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th. Weak front on 8th with isolated to scattered showers. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers and fresh to strong NW-SW winds till about the 13th. Small hail in colder air behind the front with more frequent and heavier shower activity as well as isolated cold air thunder. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk significantly with a moderate risk likely. Rainfall for the period till 15th generally 15-20mm, increasing to 25-30mm in the far south and SW coastal areas. Totals decreasing towards the N and NE down to around 10-15mm.

Western VIC

Upper low with mid-level cloud but largely remaining dry on 4th. Ridge moving in behind with initial southerly flow with some possible light showers, mainly near the SW District coastline. Cold nights from 5th to 8th with a slight to moderate frost risk, especially on 5th and 7th and especially over the Wimmera and Mallee. Weak front late on 8th and early 9th with isolated to scattered showers about the SW District and more isolated north of there. Another weak ridge moving through quickly ahead of a stronger low passing to the south of the state with multiple fronts, mostly sliding however some scattered showers at times and fresh to strong NW-SW winds till about the 13th. Small hail in colder air behind the front with more frequent and heavier shower activity as well as isolated cold air thunder about the SW District. Activity much more isolated north of the Wimmera with minimal rainfall. Another high-pressure system to move in behind this around mid-month clearing shower activity but increasing the frost risk significantly with a moderate risk likely. Rainfall for the period till 15th generally 10-18mm, increasing to 20-25mm in the far south and SW coastal areas. Totals decreasing towards the N and NE down to around 12-15mm with 3-8mm over the Wimmera and less than 1-2mm over the Mallee with many locations receiving nil.

Final Notes

• Frustrating and drawn-out break to continue with fast moving systems and low rainfall totals, however the systems will be regular but quite zonal in nature with minimal penetration northwards and east of the ranges
• Very wet for SW WA as Longwave trough drives multiple strong cold fronts into the region with good rainfall reaching the Wheatbelt
• Longwave trough to slowly shift east in second half of month bringing better rainfall opportunities firstly out of the NW-W and then the SW
• Colder air likely later in month out of the SW once the longwave trough anchors to the east of us
• July should see a return to more high pressure and weaker fronts although given the slowness through June, the start of July may see the tail end of the wetter period
• Increasing rainfall potential in spring with an attempt at a negative IOD
• Frost risk above average, not by much but certainly in any high-pressure system in current pattern. Risk increases in July a little.

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Happy Farming and Cheers from The Weatherman

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