December 2022 Outlook SA
December 2022 outlook SA
*Forecast prepared between Dec 2nd-3rd 2022
Review:
G’Day everyone, I hope you are all keeping well and trust you are very busy at this point in time making the most of the break in wet weather with some perfect harvest conditions to be had. Fingers crossed there isn’t too much damage out there and your yields can be sensational after the wet finish to the growing season. The good news is there will be more dry and hot weather for a little bit longer yet!
But looking back at November and wow what a month, it certainly had the kitchen sink of severe thunderstorms, cold, wind, hail, flash flooding and then kindly, some nice warm sunny days to finish which came just in time for many as another big system to finish may have sent some crops over the edge.
As always to be accountable, this was the November outlook:
“So overall it will come as no surprise that I am expecting another above average month for most districts, that hasn’t changed for some time now. The greatest chances of above average to well above average will be across the Lower and Upper North, Eyre Peninsula, Mallee, Riverland and into the Adelaide/Mt.Lofty Ranges region. The NE Pastoral closer to the Flinders also should do well. The greater pastoral area further north and west may become a little patchier due to the highly convective nature so there is a risk out here of some below average holes as well as the far western border portions but certainly a lot of blue again for this month. I don’t envisage the wetness of October however but still be context, it will be a frustrating month for harvest preparations and keeping crops from going rotten or sprouting in the head. Let's hope these dry days can really do some good in the meantime!”
I think overall, the month played out pretty well in terms of main focus areas plus the slightly drier holes to the NW. Perhaps the far western border areas got a bit wetter than expected though most from a large thunderstorm band where Eucla and Nullarbor had 43mm. Closer to home though, the bulk of the agricultural areas were very wet, with numerous heavy thunderstorm events, none greater than the 12th where multiple bands of thunderstorms occurred with heavy training causing flash flooding right through the Adelaide and Mt.Lofty area but also large swaths of the Lower and Upper North, especially around Spalding, Booborowie and Burra where 90-100mm fell in less than 2-3hours.
Meteorological Discussion:
So, what does this month entail? Back in September I mentioned that things would taper off in December and that certainly will occur (it already has started as you know). This drier period however will last longer than I originally envisaged with a good extra week on the cards which no doubt is a huge blessing for you all trying your very best to get the harvest done. It will also help stop any sprouting in the head and disease that may have been causing some issues so you can keep on doing what you have been!
Meteorologically, we are in a proper reset of the pattern with a relaxing of the jetstreams caused by a number of factors. The active sunspots and flares are currently no longer firing off towards earth with many now ejecting away from us. With less meandering of the jetstream means less strong upper lows and cutting off aloft with weaker dynamic forcing all round. This then has a flow on effect to the surface, so we have less intense low-pressure systems for a couple of weeks more yet but more standard troughs and wind changes which is quite typical for Southern Australia at this time of the year.
From roughly mid-December however it is likely that we will see a return to a more meridional pattern with stronger upper systems caused by that jetstream agitation however not to the levels of October or November. The dry air that will have accumulated over this reset period will temper the potential of moist inflow on the eastern side of the system with more north to south channels out of the NT/Gulf of Carpentaria.
For the meantime though we are in a fairly sedate pattern although it is mobile with stiff wind changes though minimal rainfall. A weak upper trough will push below the state on 6th squeezing the subtropical jetstream aloft generating some patchy rain areas across the West Coast/Eyre Peninsula primarily from the 5th and increasing slightly into the 6th before contracting eastwards across the northern parts of the Upper North towards the Flinders. A fresh to strong SW to S change will push in behind a surface trough early on 7th with the isobars squeezed from behind by a new bubble high in the Bight so the 7th should be a day of cooler conditions but with fresh to occasionally strong seabreezes in the afternoon, moderating later. Isolated showers more likely towards the SE districts with the trough on 7th but not a lot in it.
New high moves east quickly before another surface trough extends from the west later on the 9th crossing most districts on the 10th with isolated mid-level showers. NE to N winds will fresh ahead of this with warm to hot conditions so fire dangers may be elevated a little. Behind this trough will see a near repeat of the 7th with fresh to occasionally strong SW to S winds later 10th into the 11th and much cooler conditions once again.
A potentially more complex interaction between the cooling upper levels and the warm inland may occur around 14th-15th with isolated showers and thunderstorms, scattered inland.
Beyond this we see an increase in system potential as we round out the year with greater quantities of tropical moisture courtesy of the advancing MJO being available so I would expect at the very least an increase in shower and thunderstorm activity, with bias to an active interior.
I should also make a note that the Far North of the state (Oodnadatta etc) will see some very hot conditions in the mid 40’s as the heat that has been building across inland WA gets drawn SE ahead of these weaker changes to the south. The 6th and 10th look the two hottest days at this stage.
But overall, as an outlook for December, I am expecting a very close to average month for most areas, but perhaps with a slight trend to slight below average across agricultural areas such as the Lower and Upper North, Mallee and SE Districts but not a huge amount. Further north across the interior sees the greatest chances of above average rainfall with the upper NW Pastoral fielding the best chance of above average falls being closer to those infeeds from the NT.
Climate Drivers
The Pacific has remained a constant since the last update with minimal change in the oceans. Atmospherically though, there has been a slight eastward shift of the heavy convergence that was located across the Eastern Seaboard with much of this now channelled offshore with a focus from Eastern PNG down to New Caledonia. This area of enhanced convection co-incides both with the back end of the current MJO phase and the much warmer SST’s. We will see this type of enhancement repeat many times through the summer period with moisture then feeding back SW from this into the mainland. Once more pronounced Monsoonal Flow occurs, a lot of this will begin to channel down from the Gulf of Carpentaria into the mainland, especially QLD and NSW and also inland NT.
Now the Indian enters a period of little concern for us with its work done for 2022. The most recent MJO pulse has shredded the wind pattern that was keeping the Negative IOD in place (see Figure 4) with a mixed pattern of warmer and cooler waters with cooler now taking hold NW of Australia. This will cause a focus in convective activity to be more dominant NE of Australia rather than NW this summer for the most part although in major monsoonal bursts we will still see some strong development off WA at times but far less than QLD.
The MJO has been in phase 7 through late November to early December with a brief pass-through phase 8 before it re-emerges into the Western Indian Ocean next week. It should move steadily eastwards to reach the mainland by mid-month enhancing convection then. A monsoon flow of greater strength than the previous one is more likely towards the end of December.
The SAM has been positive although that big dominant phase is slowly coming to an end with a pullback to more neutral areas and as a result, we have some fairly stable weather. I expect most of December to see neutral values before pulling back more positive again as the next monsoon develops.
Districts:
Eyre Peninsula
Weak upper trough generating isolated mid-level showers and patchy rain chiefly over northern Eyre Pen on 5th and 6th before clearing eastwards. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Fresh to strong seabreezes. Becoming hot to very hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland towards the NW Pastoral. Rainfall for period generally less than 2-5mm over Lower Eyre Peninsula but grading to potentially 15-20mm much further north.
Upper North
Weak upper trough generating isolated mid-level showers chiefly towards the Flinders on 5th and mostly 6th before clearing eastwards. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Becoming hot to very hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland towards the Flinders and general Pastoral areas. Rainfall for period generally less than 2mm over south of the district but grading to potentially 8-12mm much further north.
Lower North
Weak upper trough with possible isolated mid-level showers in far north late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Becoming hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland. Rainfall for period generally less than 2mm over south of the district but grading to potentially 5-10mm much further north.
Yorke Peninsula
Weak upper trough with possible isolated mid-level showers in far north late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Isolated light showers possible about the foot. Fresh to strong seabreezes. Becoming hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland. Rainfall for period generally less than 2-3mm over most of the district.
Kangaroo Island
Weak upper trough late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change bring isolated onshore showers early 7th easing later as new ridge moves in. Fresh to strong seabreezes. Becoming warm to hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. Onshore flow may keep isolated light showers going through 11th-12th. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower activity although mostly north of the island at this stage with a ridge to the south keeping weather mostly stable. Rainfall for period generally less than 2-3mm over most of the district.
Adelaide Plains
Weak upper trough late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Isolated light showers possible about southern suburbs closer to the Sellicks/Willunga Hills. Fresh to strong seabreezes. Becoming hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland as ridge holds to south. Rainfall for period generally less than 2-3mm over most of the district.
Mt.Lofty Ranges
Weak upper trough late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Isolated light showers possible about southern coasts and exposed Fleurieu ranges. Fresh to strong seabreezes in the south. Becoming hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines in the south. Onshore flow may keep isolated light showers in the south going through 11th and 12th. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland as ridge holds to south. Rainfall for period generally less than 2-3mm over most of the district but possible grading to 5-6mm over exposed coasts and ranges.
Riverland/Mallee
Weak upper trough generating possible mid-level showers in far N of Riverland on 6th before clearing eastwards. But little or no rainfall. Fresh to strong SW/S change 7th easing later as new ridge moves in. Becoming hot to very hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland towards the Pastoral areas. Rainfall for period generally less than 2mm over south of the Mallee but grading to potentially 2-4mm towards the NE Pastoral Border.
Upper SE
Weak upper trough late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S about the Coorong coast and adjacent inland. Fresh to strong seabreezes. Becoming hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. Onshore flow may continue to keep isolated light showers about coastline on 11th-12th. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland as ridge holds to south. Rainfall for period generally less than 2-3mm over most of the district.
Lower SE
Weak upper trough late 5th and mostly 6th before clearing eastwards but little if any rainfall. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Isolated light showers possible about the coast and adjacent inland. Fresh to strong seabreezes. Becoming warm to hot with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers before more onshore showers move in later on 10th off the ocean. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. Onshore flow may continue to keep isolated light showers about coastline on 11th-12th. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland as ridge holds to south. Rainfall for period generally less than 2-4mm over most of the district but potentially 5-8mm falls in onshore flow about the far S coastline.
Western VIC
Weak upper trough on 6th before clearing eastwards but little if any rainfall, perhaps some coastal showers about the SW District. Fresh to strong SW/S change early 7th easing later as new ridge moves in. Isolated light showers possible about the coast of the SW District and adjacent inland. Fresh to strong seabreezes. Becoming warm to hot, especially over the Mallee with freshening NE to N winds later 9th and 10th ahead of trough with isolated thundery showers before more onshore showers move in very late 10th or early 11th off the ocean. Elevated fire dangers ahead of and with windy conditions near change. Fresh to strong SW/S winds behind this trough once again, especially about exposed coastlines. Onshore flow may continue to keep isolated to scattered light showers about coastline on 11th-12th. New ridge clearing conditions once again before complex pattern with likely upper low moving in from Bight on 13th-14th generating increasing shower and thunderstorm activity, more likely with northern extent/inland as ridge holds to south. Rainfall for period generally less than 2-4mm over most of the district but potentially 5-8mm falls in onshore flow about the far S coastline.
Finals Notes:
- Dry period lingering on with no significant rainfall before mid-month which is welcome for those harvesting
- Pattern will begin to swing back to more unstable from then on in with increasing thunderstorm potential, but more likely over the Interior
- Devastating flooding along the Murray will remain for the entire month with a peak around 1931 levels
- Still expecting much more heat to develop through Jan and especially Feb
- Drier April to May 2023 at this stage with a pointer to near positive IOD levels or weak El Nino which may lead to a stronger attempt at El Nino in 2024
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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