Funny you post this because I did dap into the charts to see what the forecasts were for the NAO/PNA. I thought that was noteworthy, but like you said ens means were not as representative as what you would expect to see in terms of pattern across the country. One thing came to mind:
As you know, the placement and structure of the anomaly centers are more important than just the chart. Here is the 12z GEFS 6-10 day mean. Excuse my terrible drawing skills but I'll try to explain what I'm getting at:
1. I wonder if the chart is being skewed by the highly anomalous High pressure center northwest of the Aleutians and the trough jut north of Hawaii. I believe this is the far western edge of the PNA domain but this could be providing enough weight to make the chart "quite negative".
2. Getting into the placement of the anomaly centers, you can see we might not be far off from significantly warmer temperatures. If the high center was more so over the Aleutians or maybe just south and the trough centered over Hawaii, would that maybe act to flatten the ridge there across the PAC NW and open the door to connect the trough over the central states with the western Arctic domain or at least tug the trough west?
With the mean trough in the West as opposed to the central we may be able connect the ridge off the coast and bring that west