The Bureau of Meteorology’s winter rainfall forecast missed the mark across large parts of southern and eastern Australia, with a season tipped to be dry instead turning out wetter than average in key cropping and grazing regions. Three months on, the Bureau’s spring outlook was updated recently with the west now carrying a wet signal, while the south-east faces a dry one. When the Bureau issued its winter outlook on 4 June, it pointed to a 60 per cent to 80 per cent chance of below average rainfall across south-west Western Australia and central and eastern regions south of the tropics, including eastern Tasmania. Parts of south-west WA and the northern and eastern Murray-Darling Basin carried an increased chance of unusually low rainfall. Just 12 days later on 16 June, the BOM officially confirmed that the El Niño-Southern Oscillation (ENSO) was in an El Niño phase, which can, but not always, mean greater chances of dry weather. What actually happened The Bureau’s seasonal summary, which was issued on 1 September, told a different story than what was forecast. National area-averaged rainfall for winter came in 8 per cent above the 1961-1990 average, with July the only drier-than-average month sandwiched between a wetter June and August. According to the report, South Australia had its sixth-wettest winter on record and its wettest since 1978, finishing 72 per cent above average. Rainfall was above to very much above average across most of SA, northern Victoria, southern WA, and much of western and central New South Wales. An area straddling the SA-NSW border recorded its highest winter rainfall on record. It should be noted that the dry signal verified in some areas. WA’s south-west and pockets of the state’s north came in below average, as did large parts of eastern Queensland and NSW, and eastern Victoria and Tasmania. Temperatures ran hot everywhere. Australia’s mean winter temperature was 1.45°C above average, equal third-highest on record, with NSW, Victoria and Tasmania all posting their warmest winters since 1910. One standout figure from the wrap: the wettest day of the season nationally was 166mm at Kirup in WA’s south-west on 2 June, right at the start of winter. Despite that single deluge, the south-west finished the season below average overall, a reminder that one big rain event early in a season doesn’t guarantee it carries through. The Bureau’s spring forecast points to different weather patterns across Australia. Below average rainfall is likely, at a 60 per cent to greater than 80 per cent chance, for the far south-west of WA, south-eastern Australia including Tasmania, parts of eastern and northern Queensland, and the northern Top End of the NT. Above average rainfall is likely, also at 60 per cent to greater than 80 per cent, across most of WA extending into western parts of the NT and SA. The Bureau notes the dry signal is strongest early, in September, before a wetter signal builds through the north from October as the wet season approaches. Southern Victoria and Tasmania are forecast to stay drier than average right through spring. A strong El Niño is now well established in the tropical Pacific and continuing to strengthen, with the Bureau’s models pointing to a peak in late spring or early summer as a very strong event. The Indian Ocean Dipole is currently neutral after briefly nudging positive, and while models suggest a positive IOD could still develop through spring, the forecast strength of that event has eased in recent runs. How much confidence to put in it The Bureau’s accuracy map for the spring rainfall outlook, based on how the ACCESS-S2 model has performed historically, shows 65 per cent to 100 per cent consistency across most of the country, including the cropping and grazing belts of eastern Australia and the forecast wet zone across WA. Confidence is lower, in the 45 per cent to 55 per cent range, in patches of central Australia near the SA-NT border and small areas of WA’s north, but those sit outside the main production regions. Given how the winter forecast played out for the south-east, that accuracy read is worth keeping in mind rather than taking the forecast pattern as settled. The Bureau itself notes El Niño’s strength in the Pacific doesn’t automatically translate to an equivalent impact on the ground in Australia. For producers weighing spring stocking decisions and feed budgets, the safest approach remains watching how the season actually tracks against these outlooks rather than planning purely on the forecast alone. The Bottom Line BOM’s winter rainfall forecast missed for southern and eastern Australia: national rainfall finished eight per cent above average, and South Australia logged its sixth-wettest winter on record. The spring outlook is forecasting above average rain for Western Australia and western SA/NT but below average rain for south-eastern Australia, including Tasmania, as a strong El Niño intensifies. BOM’s spring forecast carries 65 per cent to 100 per cent historical accuracy across most cropping and grazing regions. Track the season as it unfolds rather than plan on the outlook alone.
