Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) system is indicating below median rainfall is likely for the majority of the South-West Land Division (including the wheatbelt) for July to September 2017.

  • The SSF is indicating less than a 40% chance of exceeding median rainfall for July to September for the majority of the wheatbelt and South West. The most probable seasonal rainfall is decile 2-3. For eastern parts of the wheatbelt, chances of exceeding median rainfall are higher at 40-60%. Predictive skill based on June conditions is poor to moderate.
  • The Bureau of Meteorology’s seasonal outlook for July to September indicates the South-West Land Division (SWLD) has a 25-40% chance of exceeding median rainfall for this period. Predictive skill is moderate.
  • Temperature outlook for July to September from the Bureau indicate more than an 80% chance of above normal day-time maxima for the SWLD. Skill is moderate for most of the SWLD. Minimum temperature outlook shows a 60-80% chance of above normal night-time minima, but skill is low. There remains a risk of frost for the inland parts of the SWLD.
  • DPIRD’s SSF is also indicating no more than a 40% chance of exceeding median rainfall for July to October over northern, western and southern parts of the SWLD. The most probable four month rainfall is decile 2-3. Predictive skill based on June conditions is poor to moderate.
  • June rainfall in the South-West Land Division was very much below average, to record low totals. Maximum temperatures were above average while minimum temperatures were near average.

Three month outlook for the south-west of Western Australia

Statistical Seasonal Forecasting

DPIRD’s 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 the Seasonal Climate Information page.

The SSF forecast for July to September 2017 is indicating no more than a 40% chance of exceeding median rainfall for the majority of the SWLD (Figure 1). Over eastern parts of the wheatbelt, this has increased to 40-60% chance of exceeding median. The most probable rainfall is decile 2-3 for the majority of the SWLD, and decile 4-7 for eastern parts of the wheatbelt. Predictive skill for this period, based on June conditions, varies from poor over central and eastern parts, to moderate skill for the north and south (Figure 2). While the improvement in rainfall chances for eastern parts of the wheatbelt is encouraging, the SSF has relatively low skill for this region and time of year.

Figure 1 July to September SSF for south west WA shows a low chance of exceeding median rainfall.
Figure 1 SSF forecast of probability of exceeding median rainfall for July to September 2017
Figure 2 SSF skill map shows predictive skill over the south west of WA to vary from low skill to moderate skill.
Figure 2 Percent consistent skill of the SSF at forecasting July to September rainfall using data up to and including June

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