Seasonal — the drivers behind the pattern

Nothing on this page forecasts a day. These are the background conditions that make a run of fronts more or less likely over a fortnight to a season, and they are the context the 3–7 day charts sit inside.

CPC historical Southern Annular Mode (SAM / AAO)

Monthly historical index, 1979–present · southern winter months highlighted

Latest — Aug 2026: -0.62 — negative — leans favourable for alpine fronts · winter (Jun–Aug 2026) mean + 0.76

Southern Annular Mode monthly index, last six years Monthly AAO index. Bars below the zero line are negative SAM, which favours cold fronts reaching the Australian Alps. -2 0 2 202120222023202420252026

negative, winter (favourable) positive, winter other months

Index month Aug 2026 · fetched 1 min ago

Calculation method

The Antarctic Oscillation index from NOAA CPC, the standard measure of SAM. Positive SAM in winter shifts the westerly storm belt south, away from south-eastern Australia, so fewer cold fronts reach the Alps — the sign convention runs opposite to most readers’ intuition, which is why it is spelled out rather than just plotted. CPC now publishes this series monthly only; the daily AAO file older references cite returns 404, so this panel is monthly and does not imply finer resolution. Background

NOAA Climate Prediction Center, public domain

BoM Southern Hemisphere Monitoring

Current official ENSO, IOD and SAM monitoring

Official monitoring context, linked at source. This page deliberately does not republish the Bureau’s written commentary. Open Southern Hemisphere Monitoring.

BoM ACCESS-S outlook scenarios

These are BoM’s forecast scenarios. They are distinct from the CPC historical SAM index above: the BoM SAM graphic is an ACCESS-S forecast, while the CPC chart is observed history.

BoM Southern Hemisphere Outlooks
Bureau ACCESS-S forecast scenarios for the Relative Niño3.4 sea surface temperature index.
ACCESS-S Relative Niño3.4 outlook scenarios Issued 26 September 2026 © Bureau of Meteorology · CC BY 4.0
Bureau ACCESS-S forecast scenarios for the Indian Ocean Dipole index.
ACCESS-S IOD outlook scenarios Issued 26 September 2026 © Bureau of Meteorology · CC BY 4.0
Bureau ACCESS-S forecast scenarios for the Southern Annular Mode index.
ACCESS-S SAM outlook scenarios Issued 26 September 2026 © Bureau of Meteorology · CC BY 4.0
Bureau ACCESS-S three-month global sea surface temperature anomaly outlook map.
ACCESS-S three-month sea surface temperature outlook Issued 26 September 2026 © Bureau of Meteorology · CC BY 4.0

Not shown here, and why

These seasonal sources exist and we can reach them. What is unresolved is whether we may republish them — a licensing question, not a technical one. Each links out to the origin, which is where the community reads them today anyway.