Oregon Hikers

nwhikers.net is a Washington-centric site similar to this one.

https://www.google.com/url?sa=t&rct=j&q ... 4024,d.cGw

As others mentioned 4 days of hiking will barely scratch the surface in the NW. I'd recommend heading further north and basing your trip along either the Mt. Baker Highway, North Cascades Highway or Highway 2. You won't run out of options in any of those locations.

If you're looking for 4 days of dayhikes without a huge amount of driving then the west side of Olympic National Park might week be your best shot. You've got the coastal Olympics and the Hoh Valley in pretty close proximity. Spending one night backpacking up the Hoh would be worth it.

Alternately you could split your time between the north Oregon coast and Mt Hood.

Best weather would be between mid-July and mid-August, as long as it's not like last summer, where some storms brought in cold and wet weather up high even in mid-summer.

Get yourself to the the Alpine Lake Wilderness. There is no substitute for Washington alpine scenery. Base in Leavenworth and dayhike into Colchuck, Stuart, etc, then shoot over to Cle Elum and hike into Jade Lake on Mt Daniel and Lake Ingalls. No coast but you sound like you want the best the area has to offer. Fly into Seattle, wait till September for max snow melt. Done and done.