The daily PNA indices are shown for the previous 120 days, and the GFS forecasts of the daily PNA index at selected lead times are appended onto the time series. The indices are standardized by standard deviation of the observed monthly PNA index from 1950-2000 interpolated to the day in question. A 3-day running mean is applied to the forecast time series.

The values at the upper left and right corner of each figure indicate the mean value of the PNA index and the correlation coefficients between the observation and the forecasts, respectively.

• Time series of the difference between 15-day running mean values of the observation and the outlooks