Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) system is indicating less than 40% chance of exceeding median rainfall for May-July and May-October 2018.

  • The SSF is indicating less than 40% chance of exceeding median rainfall for the grainbelt for May to July 2018. The most probable decile range is decile 2-3 for most of the grainbelt. Predictive skill based on April conditions is mostly medium to good (60-75% consistent). In operational use since 2012, SSF has had a high success rate indicating May-July rainfall deviation across the northern and central grainbelt. The model has been less successful for the southern grainbelt and Esperance region for these three months.
  • The Bureau of Meteorology’s current seasonal outlook also indicates below normal rain being more likely, showing generally a 30-45% chance of exceeding median rainfall for May-July for the South West Land Division (SWLD). Predictive skill is mostly moderate to good (55-75% consistent).
  • Temperature outlooks for May-July 2018 from the Bureau indicate a 60-70% chance of above normal day-time maxima for the SWLD. Skill is moderate to good at 55-75% consistent. Minimum temperature outlooks indicate a 50-65% chance of above normal night-time minima for the SWLD, with skill poor to moderate at 50-65% consistent.
  • For May-October, the SSF is also indicating less than a 40% chance of exceeding median rainfall for most of the grainbelt. As for May-July, the most probable decile range is decile 2-3 for most of the grainbelt. Predictive skill is mostly moderate to good, 60-75% consistent. Since 2012 when SSF was developed, the May-October outlook has been correct in five out of six years for the northern and central grainbelt, two out of six years in the southern region and four out of six years in the Esperance region.
  • April rainfall in the SWLD was generally below average. April maximum and minimum temperatures were average to above average.
  • Current conditions are dry. Despite having summer rainfall there is little plant available soil water in most areas. It appears likely May rainfall will be below average as well. Approximately half of Australian and international climate models are indicating May-July rainfall is likely to be lower than the long term median.

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 the Seasonal Climate Information page.

For May-July, the SSF is indicating less than 40% chance of exceeding median rainfall for the grainbelt, with large parts having less than a 30% chance. The most probable decile range map indicates decile 2-3 rainfall is most likely for most of the grainbelt. Predictive skill based on April conditions is poor to good (50-75% consistent). Since 2012, SSF has had a 100% success rate in correctly indicating relative May-July rainfall in the northern grainbelt and 83% (five out of six years) in the central grainbelt. For the southern and Esperance regions the success rate is lower at 66% (four out of six years) for these three months.

SSF forecast of the probability of exceeding median rainfall for May to July 2018. Indicating a drier than normal outlook (less than 40% chance) of receiving median rainfall for the grainbelt
SSF forecast of the probability of exceeding median rainfall for May-July 2018

Percent Consistent skill of the SSF at forecasting May to July rainfall using data up to and including April. Skill is 50 to 100 percent consistent
Percent Consistent skill of the SSF at forecasting May-July rainfall using data up to and including April

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