Maybe you've come across this, but I posted this to Ray in his ENSO thread.
This is a great study and analysis on PDO state/trends and the strong correlation to forecasting prolonged heat episodes across the U.S. (in particular the SW and the East).
https://www.nature.com/articles/s41612-022-00237-7#Fig1
I find this to be one of the better studies/papers I've come across. Sometimes they can get way too involved in all the heavy math, but the analysis and explanations of everything is top notch.