April 2022 Outlook SA

 

April 2022 outlook SA

 

*Forecast prepared between Mar 31st-Apr 4th 2022

 

Review:

G’Day everyone, another month down, actually hard to believe we are now well into autumn and before we know it winter will be here.

 

A month of being stuck in between two main infeeds east and west with heavy falls and major flooding as expected sadly in NSW and also parts of QLD. Finally, WA saw some heavy falls for the first time all summer, but SA was dominated by constant ridging which was continuously re-enforced from the Bight creating stable conditions for the most part through especially Central areas. We did see the eastern border areas in the earlier part of the month come under the influence of a surface trough which generated diurnal shower and thunderstorm activity with some locally heavy falls, especially over parts of the Upper SE and also the Flinders and NE Pastoral.

 

Looking back at the March outlook I think overall it performed well for the expected pattern but underestimated the dry area a bit as it extended down a smidge more east across some parts of the Western Upper North also. See Figure 1. The anomalies as usual show it to finer detail in Figure 2 with a wider swath of slightly below average being the mainstay. The eastern border areas came up quite close to expectations. The below text was the outlook for March to recap.

 

“Overall, my outlook for March will see very close to average rainfall, slightly above in the far west and parts of the SE districts with a risk of at least average to above average rainfall this time into the NE pastoral up the border though patchy. Most other areas look about average. The main below average risk is probably over areas such as the southern NW pastoral and down through Yorke Pen and perhaps KI as well which would roughly be a zone between moisture enroaching from the west and influence from the east.”

 

 

 

Figure 1: Rainfall deciles for SA for March 2022 – source BoM http://www.bom.gov.au/climate/

Figure 2: Rainfall anomalies for SA for March 2022 – source BoM http://www.bom.gov.au/climate/

 

Meteorological Discussion:

April is now here and no doubt a very critical month for many of you wanting to get seeding done and looking for that break. We have a fairly contrasting cropping region with the Eyre and Yorke Peninsula’s likely to have good sub soil moisture but the Mallee and some areas of the Lower and Upper North being a lot less but especially anywhere east of the Ranges and down into the Upper SE. Of course, thunderstorm activity has given a few localised spots some buffer, but it does not make up the majority.

At this stage I see nothing significant on the horizon in what looks like a fairly dry month dominated by surface ridging. The curveball is this often throws up more upper troughing aloft however this will focus further east and activate rainfall over the Eastern states where the Tasman/Pacific moisture can be utilised better, especially in the form of those East Coast Lows (ECL’s).

Active sunspot activity throwing out significant CME’s will be a feature of April as well – we have already seen an X class flare in the last few days. This does cause turbulence in the earth’s jetstream so I am still open to a rogue system at some point during the month but overall, the trend is dry with that Indian summer like pattern showing up on multiple occasions.

 

Anyways moving onto current events and we have the leftovers of the strong East Coast low that brought heavy rainfall to many parts of NSW and VIC over the last few days. This low is now weakening and heading east into the Tasman. Further west middle and upper-level cloud on the satellite imagery is associated with an upper trough and this will advance eastwards in the next day or two. A weak inland trough will develop in association with this upper trough and together they will combine for some patchy rain and mid-level showers over the state on the 5th but totals will remain low due to a lack of connectivity to the tropics and strength in the overall system.

 

After this we see the re-strengthening of the high-pressure system near Tasmania which will extend a strong ridge over the state in a E/NE flow. Without surprising anyone, the upper trough from the 5^th will then stall over the eastern states and combine with a surface trough to generate showers and thunderstorms with locally heavy falls and flash flooding, with a little more inland focus this time round.

 

Further ridging will follow over SA, but a slight stirring of the westerly belt is expected around the 10^th-11^th behind the first strong high which may see a troughy system again bring mid-level showers and patchy rain areas with isolated thunderstorms in the west. A cooler kick out of the SW could follow with another strong high behind and this pattern will push right through past mid-month at this stage with a likely repeat right through a bulk of April. As mentioned, the only ‘positive’ from so much high pressure with upper troughing is the blocking that occurs and eventually a rogue cut-off may occur a bit further west than they have been occurring for the last month or two. One to watch but for now we unfortunately have to wait.

 

Consequently, my outlook for April is below average rainfall for a large swath of the state. Pockets to scattered areas of well below average are likely, especially over the Pastoral Districts once again but even down through the southern coastal districts and into the SE. The best chance of average rainfall at least is over parts of Eyre Peninsula and into the Upper North.

 

Climate Drivers

The Pacific is ever so slowly showing signs of breaking down the La Nina pattern in the oceans but the lag effect to the atmosphere will remain and as a result the moisture pile in from the east into the eastern seaboard will continue. The signs are the warming in the very far Eastern Pacific especially. Strong ridging over the SA/VIC/TAS region will essentially allow upper troughing aloft due to the block and this will in turn act to cause cyclogenesis on the east coast giving all these East Coast Lows (ECL’s) we are seeing atm. Multiple nasty little lows, with flooding, damaging wind and coastal erosion caused by large and powerful waves. This happened in 1974 with the strong La Nina, the pattern has been very classic for the east, but we are battling in the middle with the ‘overstrong’ high pressure and sinking air.

 

Figure 3: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/

No big changes in the Indian, it remains warm and a fairly active basin weather wise with plenty of convection and certainly a lot of warm water off the NW coast of WA and in the Eastern Indian in general. It bodes well for when we get a break rain but for now, the overruling pattern of dryness will remain as the downwelling/sinking air of the Hadley cell holds strong but having the Indian this warm is always better than having it cold. Refer to Figure 4 which shows the sinking air in red approaching from the west in the wake of the recent MJO pulse.

Figure 4: CHI200 index showing rising air in blues and purples and sinking air in reds and browns – source http://mikeventrice.weebly.com/mjo.html

In terms of what the IOD might do for this year, I’m seeing quite a bit of talk about a hefty negative event but I remain very cautious. Whilst there is a lof of warm water currently I do expect that to decrease as winter and spring come around. A similar level to last year is looking the leading bet at this stage whilst we have the warmth, the strength of warm east and cold west mechanism is still looking tardy so a weak negative IOD may hang around. They are not the best for consistent rainfall over Southern Australia, patchy and inconsistent more the order of the day. But this time of the year is usually very tricky to nail accurate IOD forecasts as we still have significant convection churning out over the Indian. I will review this each update given how critical this index is to SA.

 

The MJO has weakened off once it moved over the maritime continent through phases 4-5 and is now lingering very weakly in phase 6 to 7 and becoming very hard to make out. This is likely to continue now for a number of weeks with perhaps a bias to the Pacific Ocean flaring up a couple of Tropical Cyclones, the first which is already organising west of Vanuatu. This will rapidly intensify before getting sucked into the giant upper troughing that continues to induce the east coast lows and enter the Coral Sea graveyard but not before becoming quite intense – category 3 to 4 is most likely. Large swell the most likely impact on the Australian coastline.

 

The SAM is currently positive after the recent large high pressure that has been dominating the mainland and Southern Ocean giving us ridging with a SE/E flow. This will continue to be mostly positive for a week before a tick down into neutral regions as the belt of high-pressure eases off a little and we see some frontal action over the Southern Ocean/southern coastline.

 

Districts:  

 

Eyre Peninsula

Upper trough on 5^th delivering patchy rain areas before a new ridge moves in behind from the 6^th. Mostly fine conditions becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. Isolated thunderstorms in the west. More southerly flow likely behind trough bringing onshore isolated shower activity to exposed coasts with cooler conditions ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 3-5mm with isolated totals to 8-10mm possible, more likely about northern Eyre Peninsula.

 

Upper North

Upper trough later on 5^th delivering patchy rain areas before a new ridge moves in behind from the 6^th clearing activity apart from some morning patchy rain areas in the east. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers in the south ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 4-7mm with isolated totals to 8-15mm possible about elevated terrain.

 

Lower North

Upper trough later on 5^th delivering light patchy rain areas before a new ridge moves in behind from the 6^th clearing activity apart from some morning patchy rain areas in the east. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers in the south ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 3-5mm with isolated totals to 5-10mm possible about elevated terrain.

 

Yorke Peninsula

Upper trough on 5^th delivering light patchy rain areas and mid-level showers before a new ridge moves in behind from the 6^th clearing activity apart from some isolated morning showers in the east. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with cooler conditions and lingering isolated showers about the foot of Yorke Pen ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 3-5mm with isolated totals to 5-8mm possible.

 

Kangaroo Island

Upper trough on 5^th delivering light patchy rain areas and mid-level showers before a new ridge moves in behind from the 6^th clearing activity. Apart from some light morning shower activity in an onshore flow we should see mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with cooler conditions lingering and isolated showers ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 2-3mm with isolated totals to 4-6mm possible.

 

Adelaide Plains

Upper trough later on 5^th delivering light patchy rain areas and mid-level showers before a new ridge moves in behind from the 6^th clearing activity apart from some isolated morning showers. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers in the south ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 3-5mm with isolated totals to 5-8mm possible about foothills.

Mt.Lofty Ranges

Upper trough later on 5^th delivering light patchy rain areas and mid-level showers before a new ridge moves in behind from the 6^th clearing activity apart from some isolated morning showers. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated to scattered showers, chiefly about southern coasts and ranges ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 3-5mm with isolated totals to 5-10mm possible about wetter spots/higher terrain.

 

Riverland/Mallee

Upper trough later on 5^th delivering light patchy rain areas or mid-level showers before a new ridge moves in behind from the 6^th clearing activity apart from some brief morning showers. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers in the south/SW of the Mallee ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 2-3mm with isolated totals to 4-5mm possible.

 

Upper SE

Upper trough later on 5^th delivering light patchy rain areas before a new ridge moves in behind from the 6^th clearing activity apart from some isolated showers in the east and north. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers at times ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 2-3mm with isolated totals to 4-5mm possible.

Lower SE

Upper trough later on 5^th delivering mid-level showers before a new ridge moves in behind from the 6^th clearing activity apart from some isolated showers in the east and north. Mostly fine conditions with fresh SE winds at times becoming established throughout till 10^th ahead of an approaching trough around the 11^th which may bring areas of patchy rain once again. More southerly flow likely behind trough with lingering isolated showers at times ahead of further ridging by mid-month stabilising conditions. Rainfall for the period around 2-3mm with isolated totals to 4-5mm possible.

Finals Notes:

·         No breaking rains in sight yet, below average April likely

·         May potentially also a slow start but improvement likely from here on in

·         Winter seeing average rainfall for the most part

·         Weak negative IOD with cool neutral ENSO leading the bets at this stage

·         Rogue event a chance at least to break up long dry spells due to jetstream bending from strong ridging.

 

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.