I might be fishing with my son who is guiding in Ak. Probably some time in August,looking to combine trip with some time in the PNW (Oregon,Wash,Idaho) time spent would be about 1 wk and DIY. Any recommendations for steelhead water at that time, would consider a guide for a day or two.
I'd hit the North Umpqua if it were my trip - though I'm not sure how it fishes in August. You could break it up with a guided day or two on the Rogue. The Ashland Fly Shop can help you out there I'm sure.
July/August can be rough for the NU as temperatures can soar that time of year. This last year was unusual with being able to fish through the summer due to cooler temps. The Rogue is pretty much good to go year round though.
I second Velocity's comment. NU is great, but August can be a problem due to warm low water at that time. All depends on how fast the snowpack disappears in late spring/early summer. Humble Heron Fly Fishing guide service out of Grants Pass will give you a great time on the Rogue if you can be lucky enough to find them available.