Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for summer, December 2021 to February 2022 is indicating mixed chances of exceeding median rainfall for the South West Land Division (SWLD).

• For summer, December 2021 to February 2022, the SSF is indicating above 60% chance of exceeding median rainfall for parts of Central West, Central Wheatbelt and South Coastal forecast districts. Less than 40% chance for parts of South West, Great Southern and South East Coastal forecast districts. Neutral (40-60%) chances elsewhere. The most probable rainfall decile map indicates decile 2-3 for parts of South West, Great Southern and South East Coastal forecast districts. Decile 8-10 for parts of Central West, Central Wheatbelt and South Coastal forecast districts and decile 4-7 elsewhere. Predictive skill based on November conditions is mostly poor to good (50-75% consistent).
• The Bureau of Meteorology’s seasonal outlook for summer December 2021 to February 2022 is indicating 45-55% chance of above median rainfall for the majority of the SWLD.  Predictive skill is poor to good (55-75% consistent). The longer term outlook for January to March 2022 is also neutral, with wetter chances for Great Southern and South Coastal forecast districts. Skill is poor to moderate (50-65%). 
• Temperature outlooks from the Bureau for November 2021 to January 2022 indicate a 35-80% chance of above average day-time maxima (with lower chances for the Great Southern and South Coastal forecast districts). Skill is 55-75%. The Bureau indicates 60-80% chance of exceeding above average night-time minima for the SWLD. Skill is 55-75%.
• November rainfall was generally below average to average for the SWLD, but heavy falls and hail delayed grain harvest in the Central Wheatbelt and Great Southern. November maximum temperatures were below average to average and minimum temperatures were average. 
• The main climate driver influencing the SWLD is the La Niña in the Pacific. Based on past events, the SWLD is expected to have average rainfall over summer. The Southern Annular Mode remains positive, but has no influence on SWLD climate in summer.

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 on DPIRD’s Seasonal Climate Information pages for location-specific forecast information.

For summer, December 2021 to February 2022, the SSF is indicating above 60% chance of exceeding median rainfall for parts of Central West, Central Wheatbelt and South Coastal forecast districts. Less than 40% chance for parts of South West, Great Southern and South East coastal forecast districts. Neutral (40-60%) chances elsewhere. The most probable rainfall decile map indicates decile 2-3 for parts of South West, Great Southern and South East coastal forecast districts. Decile 8-10 for parts of Central West, Central Wheatbelt and South Coastal forecast districts and decile 4-7, elsewhere. Predictive skill based on November conditions is mostly poor to good (50-75% consistent).

SSF forecast of the probability of exceeding median rainfall for December 2021 to February 2022 using data up to and including November.

Percent consistent skill of the SSF at forecasting December to February rainfall using data up to and including November.

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 summer December 2021 to February 2022 is indicating 45-55% chance of above median rainfall for the majority of the SWLD.  Predictive skill is poor to good (55-75% consistent). The longer term outlook for January to March 2022 is also neutral, with wetter chances for Great Southern and South Coastal forecast districts. Skill is poor to moderate (50-65%).

Temperature outlooksfrom the Bureau for November 2021 to January 2022 indicate a 35-80% chance of above average day-time maxima (with lower chances for the Great Southern and South Coastal forecast districts). Skill is 55-75%. The Bureau indicates 60-80% chance of exceeding above average night-time minima for the SWLD. Skill is 55-75%.

Rainfall outlook for summer December 2021 to February 2022 for Western Australia from the Bureau of Meteorology

Percent Consistent skill of the Bureau of Meteorology’s outlook for December to February

The majority of other rainfall forecasting models are indicating neutral chances of exceeding median rainfall for the SWLD for summer December 2021 to February 2022.

Model distribution summary of 12 models (not including the SSF) which forecast December 2021 to February 2022 rainfall in the South West Land Division.

Recent climate

November rainfall was generally below average to average for the SWLD, but heavy falls and hail delayed grain harvest in the Central Wheatbelt and Great Southern. November maximum temperatures were below average to average and minimum temperatures were average.  

1 November to 5 December rainfall decile map for the South West Land Division. 

The atmospheric pressure In November was higher than normal over the SWLD.

Indian Ocean sea surface temperatures north-west of Western Australia are average, as the IOD has returned to neutral.The January to March 2022 SST forecast by the Bureau of Meteorology indicates SSTs anorth of WA re likely to remain average.

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. The SAM index is currently positive. In a positive SAM phase, the belt of westerly winds contracts towards Antarctica. A positive SAM phase in summer has no influence on SWLD rainfall. For more information, see the Bureau of Meteorology’s Climate Driver Update.

The Indian Ocean Dipole (IOD) has returned to neutral. As the monsoon trough shifts south over the tropical Indian Ocean, it changes wind patterns and prevents an IOD event from forming. This is why IOD events are unable to form (and therefore influence Australian climate) during the period from December to April. 

A La Niña has established in the tropical Pacific. Climate models suggest this La Niña will be short-lived, persisting until the late summer or early autumn, 2022. Based on past La Niña events, summer rainfall is expected to be average for SWLD. 

The table below summarises climate conditions in the SWLD over the past month and three-months, and can indicate what is likely to occur in the near future if climate conditions follow the current pattern.