https://www.backcountrypilot.org/me/my- ... toid=37363
https://www.backcountrypilot.org/me/my- ... toid=37364

Pass Critical Elevation Valves in the NW.
I just posted in my album a copy of a print out from the old McMinnville Oregon, MMV FSS in 2006 that lists how much weather ( ceiling ) you need to have to clear the pass by 1500 AGL based on METAR's from airports that are on both side of that pass. Standard disclaimer: Not for navigation, no claim of accuracy, for historic purposes only, stop using so much salt on your food, use your turn signals.

Back in 2006, McMinnville Oregon FSS was slated to be closed when Lockheed AFSS in Prescott AZ was opened. I always loved taking students over to our local FSS and letting them take the "5 cent tour" so they would understand how a wx briefing worked and how the system of RCO's, flight plans and SAR all worked. They were really a great bunch there.
But,... with the big FSS shut down, I knew that this was the last time it was ever going to happen. So sad. During the tour we were talking about how FSS had changed over the decades and how due to liability, certain things were going to disappear. “I sure wish I had a list of those Critical Pass Elevations you guys have..." I said. The briefer hit the print button and said "here ya go".

The list starts up near KBLI Bellingham Wa. and goes down the Cascades to the Siskiyou, Montague/Yreka Ca area ( near Mt. Shasta ). The last part of page 2 has passes along the Idaho/ West Montana area. You will notice that not all passes are included, but it is “as is”.

Friend, be safe out there. Mountain flying can be a handful. Add in a cloud ceiling and it could kill you. Don't push the weather.
Read all the books you can. Seek local advise. Take a back country flying course. Know before you go. And of course....come here to BCP.org and chat with everybody possible. All of us are willing to help you.

Safe Skies!