The daily PNA index is constructed by projecting the daily (00Z) 500mb height anomalies over the Northern Hemsiphere onto the loading pattern of the PNA. Please note that all year-round monthly mean anomaly data has been used to obtain the loading pattern of the PNA (Methodology). Since the PNA has the largest variability during the cold sesason, the loading pattern primarily captures characteristics of the cold season PNA pattern.
The daily PNA 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 of the monthly PNA index from 1950 to 2000. A 3-day running mean is applied for the forecast indices.