Jeff,
Sorry no one from the Portland area has responded. I live 85 miles south in Corvallis, Oregon so cannot help you with the greater Portland area.
We have been having a heat wave with temperatures this past week in the 90's and 100 degrees. Trying to find herps under such dry and hot conditions during daytime hours is difficult depending somewhat on the species.
I suspect that some salamanders can be located east of Portland along and in streams and seeps in the Columbia Gorge. Also, two species of garter snake are sometime associated with streams and ponds locally.
The best way to find snakes would be to know where artifical cover object are located. If I were to go out locally, it would be in the early morning hours as there is some chance of snakes being under natural and artificial cover at that time of day before it gets so warm that they retreat under ground.
The alternative is to drive back roads at night.
Richard F. Hoyer (Corvallis, Oregon)