This is the definition for the Pacific North American (PNA) index.
The Pacific North American index deals with 500mb height anomalies in the West US and into the Northeast Pacific. When we see high pressure dominating this area, we deem it to be a positive PNA. When we see storminess over the aforementioned regions, a negative PNA is in place. The positive PNA tends to lead to cold and stormy weather in the Central and East US, while the negative PNA provokes high pressure and warm weather across the same areas.
|Typical Positive PNA jet stream, and high/low pressure locations.|
|Typical Negative PNA jet stream, and high/low pressure locations.|