Having checked your location I understand the question. :-)

My hiking time in the PNW was 90% with external frame packs, where the wet stuff was strapped to the outside--problem solved. Some I.F. packs accommodate this, some not. In selecting one, either a big back mesh pocket, extendable top lid or rear/bottom lash straps/points can approximate an external-frame lash point.

If not (the single big compartment style) then isolating wet gear in a trash compactor bag and critical sleep gear and clothing in roll-top dry bags--stowed above the wet stuff--will generally get the job done. Keeping rain out of the pack is equally important and requires either an effective pack cover (pretty good except for the area around the shoulder strap yoke) or hiking in a poncho (better, but can be annoying to hike in).

Or move to California.

Cheers,