Up until a few years ago...the UKMET office issued a long-lead forecast of the North Atlantic Oscillation's (NAO) phase for the upcoming winter. The forecast was based on the correlation between May's sea-surface temperature anomalies (SSTA) in the western Atlantic ocean and the phase of the NAO. Geo-potential height anomalies at 500 mb in the same general region were also found to have predictive value.
They claimed these correlations had predictive value ~67% of the time...a far cry better than the brain-dean CW about how seasonal NAO forecasting is unpossible.
Positive height anomalies over western Europe ==> +NAO
The effect of a negative action center INVOF the Azores is unknown.
This winter's NAO signal based on the UKMET/s long-lead conceptual model is unambiguously ambiguous.
Sea-surface temperature anomalies off the NE coast suggest +NAO while SSTAs off the coast of Greenland suggest -NAO. Height anomalies at 500 mb over Greenland signal -NAO and a + NAO over western Europe. The effect of the Azores' strong negative signal is unknown.
Next up: Analogs
Earlier posts about the UKMET NAO forecast here.