Southern NSW

Date: 28 Apr 2022

Seasonal climate risk information for Southern NSW

Volume 4 | Issue 4 | 28 April 2022

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Rainfall has generally been higher over April especially in the Mallee and southern Riverina where an amazingly good start with 35mm plus will lead to timely sowing. The Central West was also wetter with 50mm plus and over 100mm around Dubbo which is now too much and making planting a challenge. Regions of the western slopes and around Albury were drier than normal up to 26 April. Modelled soil moisture is ranked wetter than normal in most areas bar the western slopes and far eastern Riverina. Soil moisture probes are still ranked unseasonably high and remained stable in most areas with rainfall equalling evaporation or plant water use.

The eastern Pacific Ocean remains cooler to depth and slightly increased in extent, capable of further La Niña activity, but the surface temperatures have become closer to normal. Trade winds are a bit stronger in the western Pacific but could be more convincing. They are still holding warmer water to our north particularly south of the Equator. Cloud patterns at the Dateline and a strengthening SOI indicate that the atmosphere is not quite ready to give up on La Niña like behaviour. Seas are very warm to Australia’s north and evaporating more moisture, lowering the pressure. Models are generally leaning towards the neutral Pacific continuing, but 4/12 models pick it back up again for a third La Niña in a row. The Indian Ocean is completely normal with basin-wide warming. Some stronger westerly wind towards Java is likely to increase warming in this region, something a number of models are predicting. All models predict a negative Indian Ocean Dipole to form in coming months, but this is an unreliable time of the year for IOD prediction. It’s also not completely obvious where the model signal is coming from. Just slightly warmer water to depth and the stronger westerly wind activity is all that can be seen at the moment.

The Southern Annular Mode has stayed positive for another month and this can have erratic effects in autumn. The stronger easterly wind seems to be more summer like in its increased rainfall effect and rain shadowing the western slopes. The lower pressure all the way to the tropics is an easy pathway for moisture to get down to SNSW.

My assessment of 12 climate models for SNSW shows likely wetter rainfall and mixed temperature predictions for the next three months.

People are reminded that in autumn, the resetting nature of the tropical oceans makes it an uncertain time for predictions for both autumn and winter. For more information about the autumn predictability barrier check out our eLearn: https://rise.articulate.com/share/laU0Fh8td92Wodvmg6M6kQZLovAJCNgx

Soil moisture

Map of Southern NSW showing plant available moisture with probes showing mainly high but stable values.
The BoM Australian Water Outlook (AWO) modelled plant available soil moisture percentages for actively growing pasture are ranked wetter at decile eight to ten, except for the western slopes and far eastern Riverina. Absolute plant available moisture has increased to 10-25 per cent in many parts. Cropping paddock soil moisture probes are essentially unchanged but show unseasonably high values and an increased chance of winter waterlogging or difficult planting. Dirnaseer increased by six percentage points from 83 to 89 per cent and Howlong decreased by four percentage points from 98 to 94. We need more soil probes to fill the gaps! If you have an internet accessible dryland probe that has an upper and lower limit established, we would love to talk to you, contact Dale Grey at the.break@agriculture.vic.gov.au

Model distribution summary for the next three months

Graphs showing nine wetter and thee neutral rainfall forecasts and two cooler, five neutral, one neutral/warmer and three warmer temperature forecasts for May to July 2022 in SNSW.
Graphs showing the distribution of 12 global model forecasts for May to July 2022 showing likely wetter rainfall and mixed temperature forecasts.

Model distribution summary for the next four to six months

Graphs showing eight wetter and one neutral rainfall forecast and six cooler and three neutral temperature forecasts for August-October 2022 in SNSW.
Graphs showing the distribution of nine global model forecasts for August-October 2022, with likely wetter rainfall and likely cooler temperature forecasts.

Model consensus forecast for the next six months

Current outlook (28 April)

Previous outlook (28 March)

May-Jul

Aug-Oct

Apr-Jun

Jul-Sep

Pacific Ocean

Slightly cool / cool
(weak La Niña)

Normal

Cool (La Niña)

Slightly cool /
normal

Indian Ocean

Warm (-IOD)

Warm (-IOD)

Slightly warmer

Warm (-IOD)

Rainfall

Wetter

Wetter

Wetter

Wetter

Temperature

Mixed

Cooler

Mixed

Mixed

Sea surface temperature anomalies

Map of the world showing sea surface temperature anomalies, a coolish Pacific Ocean with a warm Coral Sea and Indian Ocean.
The Equatorial Pacific Ocean varied over March, with NINO3 slightly cooling and NINO3.4 values slightly warming at -0.49oC and -0.62oC respectively (as of 26 April). Both these values are neutral, but the overarching horseshoe pattern of the Pacific is that of a La Niña. The ocean is warm around most of Australia and especially to our north. The whole southern Indian Ocean is warmer. The Dipole Mode Index (DMI) is currently at +0.01oC, completely normal and showing no IOD. Sea surface temperatures are the key to the world’s rainfall. For more information on how they are measured, maps created and how to read them, check out our eLearn: https://rise.articulate.com/share/kJceF16KasOxoeypJi1UWsAz0IzKKUF1

Equatorial Pacific sub-sea temperature anomalies

Cross section of the Equatorial Pacific Ocean chart showing a larger area of cool with less intensity in the east at depth.
The cool Pacific Ocean Equatorial sub-surface temperatures have increased in area to depth in April but are not as intensely cold as for March. There is still a possibility this could hang around long enough for a third La Niña in a row.

Southern Oscillation Index

Graph of the SOI shows the value is currently at +17.4
The SOI has remained strongly positive throughout April currently +17.4 (at 26 April 2022). Pressure patterns around the equator are behaving very much like La Niña with lower pressure at Darwin and higher pressure at Tahiti.

Dipole Mode Index (DMI)

Graph of the DMI shows the value is currently at +0.01oC
The DMI is the difference between the west and east boxes of ocean monitored for the IOD. The IOD is currently neutral (currently +0.01oC as of 26 April 2022), normal for this time of the year. Water in both the eastern and western boxes of the Indian Ocean is normal to warmer.

Pacific Ocean surface wind anomalies

Map showing stronger equatorial Pacific Ocean trade winds and a burst of stronger westerly Indian Ocean winds into Java.
Easterly trade winds in the Pacific have remained stronger in the western Pacific but are strongly southerly in the eastern Pacific. Continued stronger easterlies will hold the pool of warm water to Australia’s north. A region of stronger westerly winds in the Indian Ocean is further south than for a classic -IOD, but will be holding warmer water in against Java. There has been stronger easterly wind over western and coastal SNSW which is still very much +SAM like.

World cloudiness anomalies

Map of the world showing decreased cloud at the equatorial junction with the dateline and decreased cloud over northern Australia.
A lack of cloud over the international dateline junction with the equator continues and is classic La Niña-like behaviour. A large area of less cloud over the eastern equatorial Indian Ocean is due to reduced Madden Julian Oscillation (MJO) activity again this month, this has persisted over northern Australia as well. Cloud has been slightly higher over SE NSW.

Southern Annular Mode

Graph of the SAM showing weak positive values for April.
The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) has spent April mainly positive, with a few dips to neutral and just one current dip into significant negativity. A positive SAM has historically led to erratic climate effects in autumn. The dragging of systems south has led to greater easterly offshore wind flow. The NOAA and BoM models agree that the SAM will dip into moderate negativity for a short while and then bound back into weak or moderate positivity.

Air pressure

Map of the world showing the STR of high pressure at a slightly more southerly position than is usual for Autumn.
In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) continues to be further south than is normal for autumn, a hangover of both the La Niña and the positive SAM. As a result, moisture flow into SNSW is still more tropical rather than frontal like. A normal position in autumn would be centred around Adelaide, so expect to see the ridge make a move north at some stage.

Air pressure anomalies

Map of the world showing lower pressure over most of mainland Australia but normal pressure in SE SNSW.
The sub-tropical ridge of high pressure over Australia has been much lower in pressure with the South-East closer to normal. Lower pressure to our north makes it easier for moisture transport pathways and low pressure troughing to occur. Pressure is higher at Tahiti and lower over Darwin which is why the SOI is positive, indicative of La Niña like pressure conditions. The pressure differential in the equatorial Indian Ocean is the opposite of that for a negative IOD.

Modelled Climate and Ocean Predictions for Southern NSW from April 2022 run models

Twelve climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for SNSW.
Twelve climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for SNSW.
Click here to download this table in MS Word format
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