Hello,

It is likely a fungal disease attacking the tree.  The north section would stay went longer and be more prune to disease.  The south side probably dries out faster and is less problematic as a result.  Here is an article on spruce decline.  https://www.canr.msu.edu/news/what_is_spruce_decline_and_what_should_you_do_about_it#:~:text=Why%20are%20we%20seeing%20increased,regions%20in%20the%20Rocky%20Mountains.

Unfortunately, there is little that can be done.  Protective fungicide applications applied every couple weeks throughout the spring and early summer may help protect new needles as they are developing, however there is no guarantees.  Good spray coverage of the fungicide is critical.   Nothing will repair the needles that have already been infected.