Good thing you could make it back. My gf and I were heading to Nagano from Gunma on friday night. We made it about 100kms, only to have the highway closed off, and then the smaller local road blocked by a truck which had slipped. We tried taking an even smaller road, which ended up being both narrow and steep, and when the snow got too deep, we had to make a u-turn (which thank God I managed), then had to drive back another 100kms or so in the complete whiteout. Turns out we made a good call, because our other friends who were heading out to Nagano from Tokyo, got stuck in Hachioji until the next afternoon (with a 3 year old kid in the car).
Be safe. I still hope I can go this weekend though :P