Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) system is indicating less than a 40% chance of exceeding median rainfall for winter, June to August, and June to October 2018.

  • The SSF is indicating less than a 40% chance of exceeding median rainfall for the grainbelt for June to August 2018. The most probable decile range is decile 2-3 for most of the grainbelt. Predictive skill based on May conditions is mostly poor to good (50% to over 75% consistent). In operation since 2012, SSF has correctly indicated four out of six winter seasons in the northern, central and Esperance regions.
  • The Bureau of Meteorology’s current seasonal outlook is close to neutral, indicating a 40-50% chance of exceeding median rainfall for winter, June to August for the South West Land Division (SWLD). Predictive skill is mostly poor to moderate (50-65% consistent).
  • Temperature outlooks for winter, June to August, from the Bureau indicate a 60-80% chance of above normal day-time maxima for the SWLD. Skill is low to moderate at 45-65% consistent. Minimum temperature outlooks indicate a 55-80% chance of above normal night-time minima for the SWLD, with skill poor to good at 50-75% consistent.
  • For June to October, the SSF is also indicating less than a 40% chance of exceeding median rainfall for most of the grainbelt. As for winter, the most probable decile range is decile 2-3 for most of the grainbelt. Predictive skill is mostly poor to good, 50- over 75% consistent.
  • May rainfall was below to very much below average for the grainbelt, whilst the SWLD recorded it's second driest autumn (March to May) on record since comparable records commenced in 1900. May maximum temperatures were above average to very much above average in the SWLD, whilst May minimum temperatures were near average to below average.

Three month outlook for the South West Land Division

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 winter, June to August, the SSF is indicating less than a 40% chance of exceeding median rainfall for the grainbelt, with large parts having less than a 30% chance. The most probable decile range is decile 2-3 rainfall for most of the grainbelt. Predictive skill based on May conditions is poor to good (50-100% consistent). In operation since 2012, SSF has correctly indicated four out of six winter seasons in the northern, central and Esperance regions.

SSF forecast of the probability of exceeding median rainfall for June to August 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 June to August 2018.
Percent Consistent skill of the SSF at forecasting June to August 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 August rainfall using data up to and including May.

Bureau of Meteorology seasonal climate outlook

The Bureau of Meteorology’s climate outlooks are generated by a dynamical (physics based) coupled atmosphere-ocean climate model.

The Bureau of Meteorology’s current seasonal outlook has a near-neutral outlook for winter, indicating a 40-50% chance of exceeding median rainfall for the SWLD. Predictive skill is mostly poor to moderate (50-65% consistent).

Temperature outlooks for winter, June to August, from the Bureau indicate a 60-80% chance of above normal day-time maxima for the SWLD. Skill is low to moderate at 45-65% consistent. Minimum temperature outlooks indicate a 55-80% chance of above normal night-time minima for the SWLD, with skill poor to good at 50-75% consistent.

Rainfall outlook for June to August 2018 for Western Australia from the Bureau of Meteorology. Indicating 40-50% chance of exceeding median rainfall for winter.
Rainfall outlook for June to August 2018 for Western Australia from the Bureau of Meteorology.
Percent Consistent skill of the Bureau of Meteorology’s outlook for June to August rainfall. Indicating 50 to 75 percent consistent skill.
Percent Consistent skill of the Bureau of Meteorology’s outlook for June to August rainfall. 

June to October outlook for South West Land Division

For June to October, the SSF is indicating less than a 40% chance of exceeding median rainfall for the grainbelt. The most probable decile rainfall map indicates decile 2-3 is most likely for the grainbelt. Predictive skill based on May conditions is poor to good, 50-75% consistent.

SSF forecast of the probability of exceeding median rainfall for June to October 2018. This indicates low chances (mostly less than 30%) of receiving median rainfall for the period.
SSF forecast of the probability of exceeding median rainfall for June to October 2018.
Percent Consistent skill of the SSF at forecasting June to October rainfall up to and including May. Skill is 50 to 100 percent consistent.
Percent Consistent skill of the SSF at forecasting June to October rainfall up to and including May.

Recent climate

May rainfall was below to very much below average for the grainbelt. The SWLD recorded it's second driest autumn (March to May) since comparable records commenced in 1900, only behind 1914. May maximum temperatures were above average to very much above average and minimum temperatures were near average to below average. Autumn maximum temperatures were the second highest on record for the SWLD. The latest potential yield map, produced on 5 June, with a decile 5 rainfall finish indicates low yields expected in the northern and central grainbelt.

Potential yield map from 5 June 2018 indicating low potential yields for the northern and central grainbelt.
Potential yield map from 5 June 2018

In May the atmospheric pressure was much higher than normal over southern Australia. The dry autumn was due to this higher pressure causing rain bearing fronts to be pushed south of WA until late in the month. The Indian Ocean sea surface temperatures northwest and west of Western Australia are near normal.

In the tropical Pacific, the El Niño–Southern Oscillation (ENSO) remains neutral and is expected by the majority of model to remain neutral throughout the growing season.

The Indian Ocean Dipole (IOD) is also currently neutral and four out of six models are indicating it to remain neutral until October. See the Bureau of Meteorology’s IOD and Pacific Ocean interaction for details.

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 near neutral. The Bureau’s POAMA model indicates a positive SAM by mid-June. In a positive SAM event, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over southern Australia, restricting the penetration of cold fronts inland.

When major climate drivers are at neutral values, regional rainfall may be affected by more local climate conditions rather than larger-scale features. Projections of seasonal rainfall may also be variable between different models.

The table below gives a summary of past month and three month south-west Western Australia (SWWA) climate conditions, and can be used as an indication of what is likely to occur in the near future, if climate conditions follow the current pattern.

Climate indicator Past month Past three months
SWWA rainfall Below average Very much below average
SWWA mean temperature Average to above average Above average
SWWA atmospheric pressure Much higher than normal Near normal
Indian Ocean sea surface temperature Near normal Near normal
El Niño/Southern Oscillation (ENSO) Neutral Neutral
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Near neutral Negative