* The daily AO index is constructed by projecting the daily (00Z) 1000mb height anomalies poleward of 20N onto the loading pattern of the AO.

* The daily AO index and its forecasts using MRF and Ensemble mean forecast data are shown for the previous 120 days as indicated and they are normalized by standard deviation using 1979-2000 base period. A 3-day running mean is applied for the forecast indices.

* Monthly mean AO index since January 1950