Sea-effect snow, 850hPa temperatures and wind direction — the three numbers that decide your powder day.
Japan snow is a machine, not a lottery Almost all Japanese powder comes from one process: cold Siberian air crossing the warm Sea of Japan, soaking up moisture, then dumping it on the first mountains it hits. Learn the three inputs and you can call a powder day two days out. 1. Wind direction (the most important number) NW flow: the classic setup. Hokkaido's west side, Niigata and Hakuba's north end load up. N flow: favours Hokkaido and Tohoku, drier in Nagano. W/SW flow: usually warmer, wetter snow and rain risk at the base. 2. 850hPa temperature This is the temperature roughly 1,500 m up.
Below −6 °C means dry snow to the base. Between −3 and −6 °C you get quality up high, heavier down low. Above −3 °C, expect rain at village level. 3. Snowfall totals vs snow depth A 40 cm forecast on a 1 m base skis very differently from 40 cm on rocks. Check both. Our snow forecast shows daily new snow next to current depth for each region. --- The 48-hour routine 1. Two days out: check wind direction and 850hPa temp for your region.
2. One day out: check the daily new-snow table on the resort's own page. 3. Morning of: look at the live cameras. No forecast beats a photo of the trees. When two resorts show the same total, take the higher base elevation. Elevation is the difference between the best day of your trip and a wet queue. See where each region sits this week on our snow forecast page.