Looking at medium/long range models, it's really hard for a +PNA to form. Skewed toward -PDO, like we've seen 2014-2019 in the long wavelength season. The Aleutian High becomes a block in about September and the same is holding true this year.
http://mp1.met.psu.edu/~fxg1/ENSHGTAVGNH_6z/ensloopmref.html
I mention this because we had +PNA all year up until about 7-10 days ago. This -PDO is a pattern that will hold.