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.

Southern Annular Mode (SAM / AAO)

Monthly index, 1979–present · southern winter months highlighted

Latest — Jun 2026: +2.51 — strongly positive — westerlies well south, unfavourable · winter (Jun–Aug 2026) mean + 2.51

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 Jun 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

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.