A fairly easy mile or so from the trailhead, Wahclella Falls offers a scenic hike and a huge roaring waterfall. Plus a cave and rocks to scramble over, though I didn't tell you that.
All year round.
If you find any factual innaccuracies in this post, please email me via richard at thingstodoinportland dot org so I can fix it for everyone. Thanks in advance!
Go east on I-84 to exit 40; take a right and the trailhead is right there at the end of the parking lot. [Google map].