Winter '12 / '13 - North Atlantic Oscillation - November As Oracle

As it turns out...there/s a strong association between the sign of November/s monthly NAO index and the sign of the average NAO index during meteorological winter (D-J-F).  It's strongest when NOV/s NAO index is positive.

A chi-square test on NOV/s monthly values and average value of winter/s NAO suggests the sign of NOV/s NAO has a measure of predictive skill.

The 2x2 contingency counts the number of events when the the sign of winter/s NAO matched the sign of NAO in NOV.

The distribution of events offers these probabilities:
70%  + NOV ==> + Winter
30%  + NOV ==> - Winer

43% - NOV ==> + Winter
57% - NOV ==> - Winter

---
If the signs of NOV/s NAO and winter/s NAO events were independent / unrelated...then the distribution of events would follow a normal 'bell' curve where...

Positive NOV and positive (negative) winter:  15 (12) events
Negative NOV and positive winter (negative):  19 (16) events

The 2x2 contingency analysis reveals the sign of winter/s NAO is not independent (3.1% chance of Type I error) from the sign of NOV/s NAO.

---
As a footnote...OCT/s NAO has no 'predictive' value b/c it is independent from the sign of winter's NAO.

---
CPC/s monthly NAO index here.