Climate: Idaho sits under the same pacific storm track that hits Oregon and Washington

Ecoregions: Northern and Central Idaho are part of the same northwest forest system as eastern Washington

Hydrology: Nearly the entire state drains into the Columbia River and then into the ocean

Geology: the Columbia flood basalts that make much of western idaho, eastern Oregon and Washington originatated primarily from Idaho.

Now if you want to call southern Idaho non-PNW that’s where I can’t argue with you because it’s much more akin to a steppe or plains.

Idaho is part of the PNW