This winter season in Japan has been a below average and generally a non-starter with only about half as much snowfall thus far this year as we seen last year.
The upcoming weekend this theme of El Nino enhanced storms and warm weather will ring true more so than ever.
A few factors coming together will bring strong southerly winds across Taiwan and Japan by Friday into Saturday. This includes above average temperatures in southern china and a strong West Pac high for this time of year helping to funnel southerly winds north and force a upper level ridge to climb north over Japan.
This in short means lots of warm air, even on the mountains across parts of Hokoriku Saturday we are looking at rainfall or at least a rain/snow mix. Good news there is a base down so do not worry about hitting grass but for lower elevated areas it might feel more like a slushy than powder.
(SUGGESTION) The top of higher elevated mountains are your best bet. The average lapse rate or the rate temperature drops with altitude is 3.2C per 500meters. So do the math and figure out approximately how far you will need to go up if conditions are not favorable.
Good news is that by Sunday colder temperatures will move in, it depends on the strength of the wind shift though out of the north west to determine how quickly temperatures drop below zero. But by Sunday sometime morning or afternoon it will cool off to a more seasonal atmosphere.
The temperatures in Tokyo Will Climb near 20 possibly if southerly winds are strong enough by Saturday Morning.