It is more common in the south, but in the PNW west of the Cascades it works on a small scale. You would usually want to plant late August and harvest in November. The main problem is that it is hard to find seed potatoes for sale that aren't dormant at this time of year. You pretty much have to plan ahead and keep them in the refrigerator for a late planting. Wet conditions can be a problem with diseases. There is actually a whole class of specialty potatoes called diploids that are pretty much only grown in the fall in the northwest.