Hi Molly,
Unless you're just interested in "new" potatoes, the odds are against you. Our climate creates the perfect environment for late blight, a disease which spreads like wildfire with the fall rains and cooling temps. Potatoes (and tomatoes!) are highly susceptable to late blight - I've seen a whole crop of healthy plants disappear in 2-3 days! So most potato growers want to have their crop dug and cured by the time the fall rains start.

However, if you're only interested in getting a batch of fall new potatoes (the small ones the size of ping-pong balls) you could plant now and dig everything just before the fall rains. But don't try to use grocery potatoes, since they spray them with chemicals to inhibit sprouting - if you don't have a batch of strongly sprouted old potatoes laying around, you're out of luck.

BTW, potatoes are one of nature's most disease susceptable vegetables, and it's a real good idea to get your seed potatoes from a certified source. I gamble and save some of my own seed potatoes for a year or two, but then I go back to my local feed store for a new batch of certified seed and start over.

Good luck,
John