Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for July to September and July to October 2022 is indicating above 60 % probability of above median rainfall for the majority of the South West Land Division.

  • For July to September, the SSF forecast is indicating above 60% probability of above median rainfall for parts of the Central West, Central Wheatbelt, Lower West, South West and South East Coastal forecast districts, with neutral (40-60%) probability for the remainder. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Lower West, South West and South East Coastal forecast districts, decile 2-3 for part of the South Coastal forecast district and decile 4-7 elsewhere. Skill is poor to good at 50 to 70% consistent.
  • The Bureau of Meteorology’s seasonal outlook for July to September 2022 is indicating less than 40% chance of above median rainfall for the SWLD.  Predictive skill is moderate to good (55-75% consistent). The current longer-term outlook (at time of writing) for August to October 2022 is wetter 45-70%, with poor to good skill (45-75%).
  • Temperature outlooks for July to September 2022, from the Bureau indicate a 60-80% 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 60-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor at 45-65%.
  • For July to October the SSF forecast is indicating above 60% probability of above median rainfall for parts of the Central West, Central Wheatbelt, Lower West, South West, Great Southern and South East Coastal forecast districts. Less than 40% probability for South Coastal forecast district, and neutral (40-60%) probability for the remainder. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Lower West, South West, Great Southern and South East Coastal forecast districts, decile 2-3 for South Coastal forecast district and decile 4-7 elsewhere. Skill is poor to good at 50 to 70% consistent.
  • June rainfall was below average to average for the SWLDJune maximum and minimum temperatures were average to above average.
  • The main climate driver influencing South West Land Division climate is the positive Southern Annular mode, which suppresses the activity of cold fronts in the Southern Ocean, reducing rainfall to the SWLD. July rain will likely to be below average for SWLD. 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.

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 pages.

For July to September, the SSF forecast is indicating above 60% probability of above median rainfall for parts of the Central West, Central Wheatbelt, Lower West, South West and South East Coastal forecast districts, with neutral (40-60%) probability for the remainder. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Lower West, South West and South East Coastal forecast districts, decile 2-3 for part of the South Coastal forecast district and decile 4-7 elsewhere. Skill is poor to good at 50 to 70% consistent.

SSF forecast of the probability of exceeding median rainfall for July to September 2022 using data up to and including June. Indicating mixed probabilities of above median rainfall for the South West Land Division.
SSF forecast of the probability of exceeding median rainfall for July to September 2022 using data up to and including June.
Percent consistent skill of the SSF at forecasting July to September rainfall using data up to and including June. Skill is 50 to 70 percent consistent.
Percent consistent skill of the SSF at forecasting July to September rainfall using data up to and including June.

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–S2). 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 July to September 2022 is indicating less than 40% chance of above median rainfall for the SWLD.  Predictive skill is moderate to good (55-75% consistent). The current longer-term outlook (at time of writing) for August to October 2022 is wetter 45-70%, with poor to good skill (45-75%).

Temperature outlooks for July to September 2022, from the Bureau indicate a 60-80% 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 60-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor at 45-65%.

Rainfall outlook for winter July to September 2022 for Western Australia from the Bureau of Meteorology indicating 25-60% chance of above median rainfall for the SWLD.
Rainfall outlook for winter July to September 2022 for Western Australia from the Bureau of Meteorology
Percent Consistent skill of the Bureau of Meteorology’s outlook for July to September indicating 55 to 75 percent consistent skill over the SWLD.
Percent Consistent skill of the Bureau of Meteorology’s outlook for July to September

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

Model distribution summary of 12 models outlook for July to September 2022 rainfall in the South West Land Division. The majority are indicating neutral chance of exceeding median rainfall for the next three months.
Model distribution summary of 12 models outlook for July to September 2022 rainfall in the South West Land Division.

SSF Forecast for July to October

For July to October the SSF forecast is indicating above 60% probability of above median rainfall for parts of the Central West, Central Wheatbelt, Lower West, South West, Great Southern and South East Coastal forecast districts. Less than 40% probability for South Coastal forecast district, and neutral (40-60%) probability for the remainder. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Lower West, South West, Great Southern and South East Coastal forecast districts, decile 2-3 for South Coastal forecast district and decile 4-7 elsewhere. Skill is poor to good at 50 to 70% consistent.

SSF forecast of the probability of exceeding median rainfall for July to October 2022 using data up to and including June. Indicating greater than 60% probability of above median rainfall for the South West Land Division.
SSF forecast of the probability of exceeding median rainfall for July to October 2022 using data up to and including June.
Percent consistent skill of the SSF at forecasting July to October rainfall using data up to and including June. Skill is 50 to 70 percent consistent.
Percent consistent skill of the SSF at forecasting July to October rainfall using data up to and including June.

Recent climate

June rainfall was below average to average for the SWLD, due to the positive Southern Annular Mode. June maximum and minimum temperatures were average to above average.  Rainfall decile map for 1 April to 3 July 2022 shows decile 8-10 rainfall for South East Coastal, South Coastal and parts of the Great Southern and Central Wheatbelt forecast districts.

Rainfall decile map for South West Land Division 1 April- 3 July  indicating 8-10 decile rainfall for parts of the South East Coastal, South Coastal and parts of the Great Southern and Central Wheatbelt forecast districts.
Rainfall decile map for South West Land Division 1 April- 3 July  

In June the atmospheric pressure was higher than normal over the SWLD.

In June, sea surface temperatures were warmer than average around tropical Australia. The August to October, sea surface temperature outlook by the Bureau of Meteorology 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. There has been little change in the IOD in the last two months, and models have significantly over forecast a negative IOD developing since May. Models are still indicating the development of a negative IOD in July and persisting until at least October. Past negative IOD events generally increase rainfall in the eastern grainbelt.

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 which suppresses the activity of cold fronts in the Southern Ocean. SAM forecast to remain positive until the end of July. For more information see the Bureau of Meteorology’s Climate Driver Update.

The 2021-22 La Nina is at an end, with key indicators having returned to neutral. However, some models suggest that La Nina may re-from during spring 2022.

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.

Climate Indicator Past month Past 3 months
SWLD Rainfall Below average to average Mixed
SWLD Mean Temperature Average to above average Average to above average
SWLD atmospheric pressure Higher Lower
Indian Ocean Sea surface temperature Warmer Warmer
El Niño/Southern Oscillation (ENSO) neutral La Niña
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Positive Positive