Pick a resort and you get two ensemble forecasts for it, two weeks ahead — the American model (GFS, 31 runs) and the European one (ECMWF, 51 runs), each run many times from slightly different starting data. Where the runs agree, the forecast is trustworthy. Where they spread apart, it isn't. The shaded band on each chart is that spread, so you can read the confidence directly instead of squinting at overlapping lines.
Below the charts are live webcams. If it's dark at the resort — which it usually is for Japan when you're looking from the UK — the cams fall back to the last frame captured in daylight, and the timelapse button plays the day through.
A model doesn't update continuously: it runs a few times a day — 00z, 06z, 12z, 18z — from a fresh snapshot of the atmosphere, and takes several hours to arrive after that. Between runs nothing here changes; when a new one lands the charts can shift. Each forecast says which run it is drawn from and when the next is due. Forecast data from Open-Meteo (GEFS 0.5° and ECMWF IFS ensemble 0.25°).