Okayama is a bit further South than the central areas, but if you want to go skiing from either there or direct from Tokyo there are a few ways you can go about it. Hokkaido, the Northern most area of Japan is always a great place to visit, but you would need to take a flight out of Okayama and back to Tokyo.
Nagano would be a closer bet, and there are plenty of ski resorts in the area, including in Hakuba, just an hour or so from Nagano station. To get there, you can take a bullet train from Okayama to Nagoya and then switch lines to Nagano (most resorts will have shuttles from Nagano station if you call ahead). Or you can leave from Tokyo directly to Nagano.