If still viable (unfrozen) probably wouldn't care about being carefully dug and stored now. Might work better to wait until spring to divide, though.

We covered ours with plastic and then a 6" layer of straw today. We did the same last year, but earlier in the season. Better late then never. I'm going to try digging very early in spring and dividing then. We have always dug them up before, but then you have to deal with storing, and that is getting a bit hard.

I don't like working wet soil. I have some under plastic to dry out the soil before digging.

Treepalm, for storage you need to just try the Saran wrap method. You'd be amazed. With proper prep of tubers, it's not quite, but close to fool proof. People who have failed at it won't say so, but I am sold lock, stock, and barrel. I have all my divided tubers from 250 plants in 4 styrofoam coolers, maybe 5. Stacked up and waiting for spring.

Chartreuse: you can dig anytime. I was out in 22 degrees trying to untie frozen ties in October, then trying to dig up 20 lb clumps of entirely soaked roots in November. I think if I were in Seattle proper, I would do as Treepalm said, and just mulch well and do the digging in Spring. It's no fun unearthing heavy sodden clumps of dahlia tubers, harder on the tubers too.