Seasonal Climate Outlook

SSF Forecast for May to October

 

For June to October, the SSF is indicating less than a 40% chance of above median rainfall for parts of the Central West, Central Wheatbelt and South East Coastal Districts, with neutral odds elsewhere. The most probable rainfall decile map indicates decile 2-3 for the Central West, Central Wheatbelt and South East Coastal Districts. Decile 4-7 rainfall is forecast for the remainder of the SWLD. Predictive skill based on June conditions is poor to good (50 -75% consistent).

SSF forecast of the probability of exceeding median rainfall for June to October 2020 using data up to and including May. Indicating a below 40% chance of exceeding median rainfall for the parts of the northern and eastern grainbelt and Esperance shire.
SSF forecast of the probability of exceeding median rainfall for June to October 2020 using data up to and including May.
Percent Consistent skill of the SSF at forecasting June to October rainfall using data up to and including May. Skill is 50 to 100 percent consistent.
Percent Consistent skill of the SSF at forecasting June to October rainfall using data up to and including May.

Recent climate

May rainfall was generally below average across cropping regions, though some parts in the south and around Merredin received decile 8-9 rainfall. Autumn, March to May, rainfall was below average in the north and only near average in the south-west corner. Autumn rainfall in the SWLD has been below average since 2017. May maximum temperatures were average to above average. May minimum temperatures were below average to average. Rainfall from 1 April to date has generally been below average in the SWLD.

Rainfall deciles for 1 April to 7 June 2020 in the South West Land Division. Indicating below average rainfall for the majority of the SWLD.
Rainfall deciles for 1 April to 7 June 2020 in the South West Land Division.

In May, the atmospheric pressure was higher than normal over the SWLD.

Indian Ocean sea surface temperatures (SST) north-west of Western Australia have been warmer than average, though they have cooled recently. While SSTs remain warmer than average, their influence on Australian rainfall has been waning. The July to September 2020, SST forecast by the Bureau of Meteorology indicates SSTs are likely to remain warm north of WA.

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 Southern Annular Mode (SAM) is currently positive and is forecast to be remain positive in June. During winter, a positive SAM typically means less rainfall for SWLD.

The Indian Ocean Dipole (IOD) is currently neutral. Four out of six international climate models surveyed by the Bureau suggest the development of a negative IOD by the end of July, to last through to October. Note that these models have low skill in forecasting IOD at this time of the year. Winter-spring rainfall in the SWLD has been on average decile 5-6 for the past nine negative IOD events. However, not all negative IOD events have brought rain to the SWLD; 2010 and 2016 were both negative IOD years.

Mean winter-spring rainfall decile map of nine negative Indian Ocean Dipole years. The mean rainfall decile of these years is decile 5-6 in the South West Land Division.
Mean winter-spring rainfall decile map of nine negative Indian Ocean Dipole years.

The El Niño–Southern Oscillation (ENSO) is likely to remain neutral over winter, some models are indicating a possible La Niña developing in late spring. For further information, see the Bureau of Meteorology’s ENSO Wrap Up.

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 Average to Below Average Mixed
SWLD Mean Temperature Average Above Average
SWLD atmospheric pressure Above Average Near Normal
Indian Ocean Sea surface temperature Warmer Warmer
El Niño/Southern Oscillation (ENSO) Neutral Neutral
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM)  Positive Positive