South Australia

Seasonal climate risk information for South Australia

Volume 3 | Issue 3 | 27 March 2020

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We are describing the cropping areas of South Australia broadly as south of a line starting at Ceduna to Pt Augusta and down to Renmark. Uses of the term’s east and west in this region refer to Port Augusta as a reference, or north and south of Adelaide. Local regions will be used if the models are more specific.

It’s been a relatively benign month for rainfall with few significant changes in stored soil moisture across South Australia.

Oceans to the north of Australia are still capable of providing more moisture. Most models predict these warmer waters to hang around for some time.

In the Central Pacific, things are primed with generally more cool water than warm, from which four models are getting sniffs of a possible La Nina. The Trade Winds are also blowing a bit stronger which would need to happen for a La Nina to form later this year. Cloud patterns have come back from being El Nino like, to normal and pressure patterns are also normal. History tells me anything could happen in the Central Pacific from now on.

The Indian Ocean is just warm all over, with no phenomena apparent. Three models predict a negative IOD could pop up in late winter, but it’s very early for them to be making predictions about that, given IOD predictability isn’t very good this far out. Their signals are probably coming from a patch of undersea warmer water off Indonesia – so we’ll be watching that over the coming months.

Rainfall trigger mechanisms have shown drier tendencies. The SAM has been weakly positive and while it’s erratic in autumn, a neutral or negative SAM would fill you with more frontal confidence.

Pressure patterns are now in a summer pattern, not ideal for autumn and are forcing fronts and lows further south, where pressure has been higher, leading to stable weather over SA for much of the month.

Interestingly, there are some sniffs of “wetter” from many models. Tantalisingly, these suggestions of “wetter” continue into the four to six-month outlook period, but at this time of the year it’s just eye candy. For the near term, on balance, most models are split between neutral (anything could happen) and wetter being more likely and neutral temperatures (anything could happen).

Do you want to hear the latest science, insights and innovations happening in the climate and agriculture space?  Then the 2020 Climate Webinar series is where you will hear from the experts from Agriculture Victoria, BoM, CSIRO and other agencies.  The series will run during lunchtime or you also have the option to listen to recordings at a time that suits.  The next webinar is:

Seasonal climate outlooks for Victoria, South Australia, Tasmania and Southern New South Wales. Dale Grey, Seasonal Risk Agronomist, Agriculture Victoria

Date: 10 am or 12 pm Wednesday 15 or Friday 17 April all South Eastern States.

Dale will explain in greater detail (45 minutes instead of 4 minutes) what the climate drivers and indicators are up to and predictions for winter and spring.

visit: http://agriculture.vic.gov.au/agriculture/weather-and-climate/climate-webinars
email: heather.field@agriculture.vic.gov.au

Soil moisture

map of SA showing soil moisture probes measurements.

The BoM Australian Water Resources Assessment (AWRA) modelled plant available soil moisture (10-100cm) predicts that moisture has decreased during the month due to evaporation and pasture growth. The soil moisture probes (courtesy of NR-SAMDB, EPARF, SARDI, AgByte and MFMG) still show that the November, January and February rainfalls have been maintained with weed control. A recent storm in the upper EP boosted Kimba by 21% and Pinkawillinie by 8% (yellow sites increased by greater than 10%). Hoyleton, Waikerie and Bordertown have decreased by 10, 15 and 16% respectively (red sites decreased by greater than 10%). Most other sites have had no change or small decreases.

Model distribution summary for the next three months

Graphs showing the distribution of global model forecasts for December-February, with models showing increased chances of drier rainfall and warmer temperature.

Model distribution summary for the next four to six months

Graphs showing the distribution of March-May forecasts with models showing increased chances of average rainfall and warmer/average temperatures.

Model consensus forecast for the next six months

Current outlook (to 27 March)

Previous outlook (to 28 February)

Apr-Jun

Jul-Sep

Mar-May

Jun-Aug

Pacific Ocean

Slightly warm

Slightly cooler/ neutral

Slightly warm

Slightly cooler

Indian Ocean

Slightly warm

Slightly warm

Slightly warm

Slightly warm

Rainfall

Neutral/ slightly wetter

Slightly wetter

Average

Average/ slightly wetter

Temperature

Neutral

Neutral

Average

Average

Sea surface temperature anomalies

Equatorial Pacific Ocean Sea surface temperatures and the IOD are at neutral levels.

Oceans to our north and south of the Equator are warmer than normal by some 0-5-1.5oC and are an enhanced moisture source. Current value of the Dipole Mode Index is -0.07oC (as of 25 March) which is neutral, as is normal for this time of the year. Sea surface temperature (SST) anomalies along the Equatorial Pacific cooled and then rewarmed to be unchanged for the month, currently at neutral temperatures. NINO3 is at +0.47oC and NINO3.4 is +0.63oC (as of 26 March).

Equatorial pacific sub-sea temperature anomalies

Equatorial undersea temperature anomalies in the Pacific have shown little change for some months.

The Pacific Ocean Equatorial sub-surface temperatures anomalies have lost some warmth in the western Pacific this month. The cooler anomaly underneath the western Pacific has cooled further. Trade wind activity along the Equator, effected by tropical weather will dictate where the Pacific undersea heads in coming months.

Southern oscillation index

The SOI value is currently at +0.1 (as at 11 February).

The SOI remains in neutral territory, currently at -0.7 (as at 25 March). Pressure patterns around the Equator as measured by this index are normal. The SOI will be worth watching once the northern wet season is over, usually by late April.

Pacific ocean surface wind anomalies

The Equatorial trade wind are reversed off PNG but are stronger in the Central Pacific.

In February there was some reversal of the easterly Trade Winds near PNG, but during March this disappeared. The trade winds have remained slightly stronger in the Central Pacific. If this continues, cooling of the surface would most likely occur.

World cloudiness anomalies

Cloud is abundant over the Dateline and lacking to the north of Australia.

Cloud at the International Dateline (180oW) junction with the Equator has been slowly returning from high (blue colour) to more normal values.  This has probably been because the weak reversed Trade Wind feed into the Dateline has stopped, which was leading to El Nino like cloud patterns. If the trade winds stay stronger, expect less cloud in this region. Cloud is still lower to our tropical north due to higher pressure, but moister air is in abundance. There has been more cloud over southern Australia.

Southern annular mode

the SAM had spent most of November in strong negativity.

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) has been weakly positive through March. In winter, a positive SAM can drag fronts away from southern Australia but during autumn SAM can have a variable effect on our climate. The NOAA 14-day forecast predicts the SAM to stay at similar values for a week and return to normal.

Air pressure

the STR of high pressure has been slightly higher than its normal summer position of Melbourne.

In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) has stayed at a summer position situated over Melbourne. This pattern can start to block triggers to rainfall. Now that we are in autumn, we hope to see a northward migration of the pressure ridge at some time. This would indicate greater chances of frontal systems coming through. A pressure ridge off South-West Western Australia has been slowly propagating its way eastwards for many months. This has led to stable, dry conditions for the lower EP, YP and SE districts, by squeezing frontal systems further south.

Air pressure anomalies

Pressure at Darwin and Tahiti is slightly higher which is why the SOI is neutral. Victoria has seen lower than average pressure.

The Sub Tropical Ridge of High Pressure had been lower, but has recently gone stronger, and much more so to the south west of SA, indicative of stable weather particularly in southern areas. The pressure is slightly higher at Darwin and normal at Tahiti. The SOI is normal.

Modelled Climate and Ocean Predictions for South Australia from March 2020 run models

12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for Tasmania

Click here to download this table in MS Word format
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