I'd agree with shizen ...
definitely pot them up, but keep them in a place that will get cold but not severely so. Possibly mulch the pots with leaves or pine boughs, or keep them in a enclosed space with some air circulation. Although iris are dormant, as far as leaves and rhizome development go, there still can be root activity, developing and growing, so potting them will give them a chance to continue to root establish until you get them into the ground come spring time, or after all danger of hard, deep freezes past. As shizen said, water just enough to keep the soil barely moist or as needed.
I'm in eastern Oregon, and although we don't get the precip you do, it does get cold here.