I have compiled the 8 years of Niseko snow data from the snowjapan.com website and Jim in Tokyo is absolutely right about timing. FYI the monthly pattern with December/January concentration is exactly the same in Hakuba, just an overall lower average of ~375 inches vs. ~575 in Niseko.
Average Niseko monthly snowfall in inches:
This is an unusual pattern by North America/Alps standards. I doubt you could find mountain resorts here where average March snowfall is only half of January's. Most places they are not too different, and many places in Colorado March averages more snow than January.
Most of Japan has weather like similar latitude on U.S. East Coast. It is not dry in the summer; I was there 9 days in July 2009 and climbed Mt. Fuji in the rain and fog. If snowfall decreases it's a safe bet it's not being replaced by a lot of sunny days, more likely an increase in rain. Lift served altitudes are low, 1,000-4,000 feet in Hokkaido at ~42 degrees latitude and 4,000-7,000 at ~36 degrees latitude in Hakuba. For the backcountry types in spring the Japan Alps behind Hakuba go up to 10,600 and Mt. Fuji is 12,300.
I will be making my first ski trip to Japan Jan. 17-31. I will be with http://www.blackdiamondtours.com/ and hope to get some of the exploration Tengu recommends with their guidance.
Edited by Tony Crocker - 12/15/10 at 4:46pm