Seasonal Climate Outlook

Summary

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

• For May to July 2022, the SSF is indicating below 40% probability for the South Coastal and South East Coastal forecast districts, above 60% for parts of the Central West and Central Wheatbelt, South West and western part of the Great Southern forecast districts. With neutral (40-60%) probability elsewhere. The most probable rainfall decile map indicates decile 2-3 for South Coastal and South East Coastal forecast districts. Decile 8-9 for parts of the Central West, Central Wheatbelt, South West and western part of the Great Southern forecast district. Decile 4-7 elsewhere. Predictive skill based on April conditions is moderate to good (60-100% consistent).
• The Bureau of Meteorology’s seasonal outlook for May to July 2022 is indicating neutral (40-55%) 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 winter June to August 2022 is also mostly neutral, with lower chances (35-45%) for the northern grainbelt, with moderate to good skill (55-75%).
• Temperature outlooks for May to July 2022, from the Bureau indicate a 45-80% chance of above average day-time maxima, with the higher chances along the coast. Skill is 75-100%. For night-time minima for the SWLD, the Bureau is indicating 55- 80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor mostly at 45-55%.
• The SSF forecast for SWLD May to October 2022 rainfall is indicating less than 40% probability of above median rainfall in South Coastal, South East Coastal and coastal parts of the Lower West and southern coastal parts of the Central West forecast districts. Above 60% for parts of the Central West, Central Wheatbelt and South West and western part of the Great Southern forecast districts, with neutral probability elsewhere. The most likely decile range map is indicating decile 2-3 for South Coastal and South East Coastal forecast districts. Decile 8-9 for South West, western part of the Great Southern, parts of the Central West and Central Wheatbelt forecast districts. Decile 4-7 elsewhere. Skill is poor to good at 50 to 75 % consistent.
• April rainfall was average to above average for the SWLD. Munglinup in the South East Coast forecast district, received 230 mm of rain.  April maximum temperatures were mostly below average, with minimum temperatures average. 
• The main climate drivers influencing South West Land Division climate is the positive Southern Annular mode, which may suppress the activity of cold fronts in the Southern Ocean. Models indicate a negative Indian Ocean Dipole developing in May and persisting until at least September. This would bring increased rainfall to the eastern grainbelt and cooler days in the south, however there is low confidence in the skill of the models at this time.

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 May to July 2022, the SSF is indicating below 40% probability for the South Coastal and South East Coastal forecast districts, above 60% for parts of the Central West and Central Wheatbelt, South West and western part of the Great Southern forecast districts. With neutral (40-60%) probability elsewhere. The most probable rainfall decile map indicates decile 2-3 for South Coastal and South East Coastal forecast districts. Decile 8-9 for parts of the Central West, Central Wheatbelt, South West and western part of the Great Southern forecast district. Decile 4-7 elsewhere. Predictive skill based on April conditions is moderate to good (60-100% consistent).

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

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

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 May to July 2022 is indicating neutral (40-55%) 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 winter June to August 2022 is also mostly neutral, with lower chances (35-45%) for the northern grainbelt, with moderate to good skill (55-75%).

Temperature outlooks for May to July 2022, from the Bureau indicate a 45-80% chance of above average day-time maxima, with the higher chances along the coast. Skill is 75-100%. For night-time minima for the SWLD, the Bureau is indicating 55- 80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is poor mostly at 45-55%.

Rainfall outlook for May to July 2022 for Western Australia from the Bureau of Meteorology indicating 40-55% chance of above median rainfall for the SWLD.

Percent Consistent skill of the Bureau of Meteorology’s outlook for May to July

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

Model distribution summary of 12 models outlook for May to July 2022 rainfall in the South West Land Division.

SSF Forecast for May to October

The SSF forecast for SWLD May to October 2022 rainfall is indicating less than 40% probability of above median rainfall in South Coastal, South East Coastal and coastal parts of the Lower West and southern coastal parts of the Central West forecast districts. Above 60% for parts of the Central West, Central Wheatbelt and South West and western part of the Great Southern forecast districts, with neutral probability elsewhere. The most likely decile range map is indicating decile 2-3 for South Coastal and South East Coastal forecast districts. Decile 8-9 for South West, western part of the Great Southern, parts of the Central West and Central Wheatbelt forecast district. Decile 4-7 elsewhere. Skill is poor to good at 50 to 75 % consistent.

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

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

Recent climate

April rainfall was average to above average for the SWLD. Munglinup in the South East Coast forecast district, received 230 mm of rain.  April maximum temperatures were mostly below average, with minimum temperatures average. The break of season map indicates an early break for the majority of the South West Land Division, with some locations in the northern and central grainbelt, still waiting for a break (haven’t received 15 mm over 3 days since 1 April).

Break of season map for the South West Land Division for the 1 May.

In April the atmospheric pressure was normal over the SWLD.

In April, sea surface temperatures were warmer than average around tropical Australia. The May to July, sea surface temperature outlook by the Bureau of Meteorology indicates SSTs are likely to remain warmer than normal around Western Australia, indicating the possibility of the development of a negative Indian Ocean Dipole.

The Indian Ocean Dipole (IOD) is neutral. Models are indicating the development of a negative IOD in May and persisting until at least September at this stage. Past negative IOD events generally increase rainfall in the eastern grainbelt and bring cooler days to the south. However, model outlooks issued at this time of the year have low skill beyond autumn.

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 and expected to remain positive until mid-May before returning to neutral. A positive SAM in autumn may suppress the activity of cold fronts in the Southern Ocean. For more information see the Bureau of Meteorology’s Climate Driver Update.

The 2021–22 La Niña event continues to weaken. However, atmospheric indicators remain above La Niña levels, continuing it’s influence, mostly on eastern Australian climate. Majority of models indicate a return to neutral ENSO conditions by June.

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.