Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for winter, June to August, 2022 and June to October 2022 is indicating below 40% probability of above median rainfall for parts of the Central West, Central Wheatbelt, Great Southern, South Coastal and South East Coastal forecast districts, with higher probabilities for the remainder of the South West Land Division.

• For winter, June to August, the SSF forecast is indicating less than 40% probability of above median rainfall in parts of the Central West, Central Wheatbelt, Great Southern, South Coastal and South East Coastal forecast districts. Above 60% for western parts of the Great Southern and South West forecast districts, with neutral probabilities elsewhere. The most likely decile range map is indicating decile 2-3 for large part of the SWLD, decile 8-9 for eastern part of Central West, western part of the Great Southern and the South West forecast districts and decile 4-7 elsewhere. Skill is poor to good at 50 to 75 % consistent.
• The Bureau of Meteorology’s seasonal outlook for winter, June to August, 2022 is indicating less than 40% chance of above median rainfall for the SWLD.  Predictive skill is moderate to good (55-100% consistent). The current longer-term outlook (at time of writing) for July to September 2022 has higher chances (45-70%), with moderate to good skill (45-75%).
• Temperature outlooks for winter, June to August 2022, from the Bureau indicate a 45-80% chance of above average day-time maxima, with the higher chances along the coast. Skill is 65-75%. For night-time minima for the SWLD, the Bureau is indicating 45-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor at 45-65%.
• The SSF forecast for SWLD June to October 2022 rainfall is indicating less than 40% probability of above median rainfall in parts of the Central West, Central Wheatbelt, Great Southern, South Coastal and South East Coastal forecast districts. Above 60% for western parts of the Great Southern and along the southern coast of the South West forecast district, with neutral probabilities elsewhere. The most likely decile range map is indicating decile 2-3 for large part of the SWLD, decile 8-9 for western part of the Great Southern and the South West forecast districts and decile 4-7 elsewhere. Skill is poor to good at 50 to 100 % consistent.
• May rainfall was mostly average for the SWLD. May maximum temperatures were average to above average, with minimum temperatures average. 
• The main climate drivers influencing South West Land Division climate is the positive Southern Annular mode, which often has a drying influence. Models are indicating the development of a negative IOD in July and persisting until at least October at this stage. Past negative IOD events generally increase rainfall in the eastern grainbelt. Outlook accuracy begins to significantly improve during June.

Three Month Outlook for the south-west of Western Australia

Statistical Seasonal Forecasting (SSF)

DPIRD’s Statistical Seasonal Forecast (SSF) system uses historical relationships between global sea surface temperature and sea level pressure with rainfall in south-west Australia to produce forecasts of rainfall for the coming months. Users can click on any station indicated on the map for location-specific forecast information from DPIRD’s Seasonal Climate Information [1] pages.

For winter, June to August, the SSF forecast is indicating less than 40% probability of above median rainfall in parts of the Central West, Central Wheatbelt, Great Southern, South Coastal and South East Coastal forecast districts. Above 60% for western parts of the Great Southern and South West forecast districts, with neutral probabilities elsewhere. The most likely decile range map is indicating decile 2-3 for large part of the SWLD, decile 8-9 for eastern part of Central West, western part of the Great Southern and the South West forecast districts and decile 4-7 elsewhere. Skill is poor to good at 50 to 75 % consistent.

[2]

SSF forecast of the probability of exceeding median rainfall for June to August 2022 using data up to and including May.

[3]

Percent consistent skill of the SSF at forecasting June to August rainfall using data up to and including May

Bureau of Meteorology seasonal climate outlook

The Bureau of Meteorology's climate forecast system for monthly and seasonal climate outlooks is the Australian Community Climate Earth-System Simulator – Seasonal (ACCESS–S [4]2). It is a dynamical (physics-based) forecast modelling system and is a collaboration between the Bureau of Meteorology and the UK Meteorological Office.

The Bureau of Meteorology’s seasonal outlook for winter, June to August, 2022 is indicating less than 40% chance of above median rainfall for the SWLD.  Predictive skill is moderate to good (55-100% consistent). The current longer-term outlook (at time of writing) for July to September 2022 has higher chances (45-70%), with moderate to good skill (45-75%).

Temperature outlooks for winter, June to August 2022, from the Bureau indicate a 45-80% chance of above average day-time maxima, with the higher chances along the coast. Skill is 65-75%. For night-time minima for the SWLD, the Bureau is indicating 45-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor at 45-65%.

[5]

Rainfall outlook for winter, June to August, 2022 for Western Australia from the Bureau of Meteorology

[6]

Percent Consistent skill of the Bureau of Meteorology’s outlook for June to August  

Looking at other rainfall forecasting models, the majority of models are indicating neutral chance of exceeding median rainfall for the SWLD for winter, June to August, 2022.

[7]

Model distribution summary of 13 models outlook for June to August 2022 rainfall in the South West Land Division.

SSF Forecast for June to October

The SSF forecast for SWLD June to October 2022 rainfall is indicating less than 40% probability of above median rainfall in parts of the Central West, Central Wheatbelt, Great Southern, South Coastal and South East Coastal forecast districts. Above 60% for western parts of the Great Southern and along the southern coast of the South West forecast district, with neutral probabilities elsewhere. The most likely decile range map is indicating decile 2-3 for large part of the SWLD, decile 8-9 for western part of the Great Southern and the South West forecast districts and decile 4-7 elsewhere. Skill is poor to good at 50 to 100 % consistent.

[8]

SSF forecast of the probability of exceeding median rainfall for June to October 2022 using data up to and including May

[9]

Percent consistent skill of the SSF at forecasting June to October rainfall using data up to and including May.

Recent climate

May rainfall was mostly average for the SWLD. May maximum temperatures were average to above average, with minimum temperatures average.  Rainfall decile map for 1 April to 5 June 2022 shows decile 8-10 rainfall for South East Coastal and parts of the Great Southern, Central Wheatbelt and Central West forecast districts.

[10]

Rainfall decile map for South West Land Division 1 April-5 June

In May the atmospheric pressure [11] [11]was below normal over the SWLD.

In May, sea surface temperatures [12] were warmer than average around tropical Australia. The July to September, sea surface temperature outlook by the Bureau of Meteorology [13] indicates SSTs are likely to remain warmer than normal around Western Australia and the north and south-east of Australia.

The Indian Ocean Dipole (IOD) is neutral. Models are indicating the development of a negative IOD in July and persisting until at least October at this stage. Past negative IOD events generally increase rainfall in the eastern grainbelt. Outlook accuracy begins to significantly improve during June.

The Southern Annular Mode (SAM), also known as the Antarctic Oscillation (AAO), describes the north–south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the southern hemisphere. SAM is currently positive (but went negative in late May) which may suppress the activity of cold fronts in the Southern Ocean. SAM is forecast to be negative by 12 June and then return to neutral until the beginning of July. For more information see the Bureau of Meteorology’s Climate Driver Update [14].

The La Niña remains active in the tropical Pacific Ocean. Majority of models indicate a return to neutral ENSO conditions by July.

The table below gives a summary of past month and three-month South West Land Division (SWLD) climate conditions, and can indicate what is likely to occur in the near future if climate conditions follow the current pattern.