How do you read a Hokkaido snow forecast? 西西's pre-trip routine

This is how 西西, SnowWind’s vice principal, picks a resort.

This post is useful if you:

• are planning a trip and want to know on which day, and at which resort, the snow will be deeper
• can read a precipitation forecast but do not know how to turn it into a picture of the powder
• want to know what is still left for you to judge after you have read the forecast

The process comes from 西西’s teaching notes. The websites’ interfaces and forecast models can change at any time; this post describes them as they were when 西西 wrote the notes.

西西’s three-step process

When 西西 was planning a Hokkaido trip for a friend, the two of them spent a long time debating where to ride. 西西 turned the filtering into the three steps below.

Step 1: SnowJapan — which resort has the most snow on the ground.

On SnowJapan, search for Daily Reports and open the Snow Depth Table. It ranks the resorts by their current snow depth.

西西 points out one thing about reading it: the depth on the table is how far a probe goes in after the resort has groomed the snow. 西西’s example: one day Kamui Ski Links showed 115 cm on the table, while about 2.5 m of snow had actually fallen in Asahikawa that season. (The post does not give the year.)

Step 2: Windy — the snow on the day you arrive.

On Windy, search for the resort and choose the snow depth layer: green means shallow, yellow means moderate, red means deep.

The key move is dragging the timeline to the time you will reach the resort. If the area turns from yellow to red, the snow will be at its deepest when you arrive.

Step 3: Precipitation — then do the conversion yourself.

西西 reads the precipitation (Rain) row on Windy, estimates how much will fall in the few hours before arrival, and pictures how much new snow that lays on the surface.

Precipitation is not snowfall. To convert one into the other you need the snow-liquid ratio, and the snow-liquid ratio changes with temperature. The concept is covered in The Science of Powder, Part 2. That post also points out that the snowfall field in most weather APIs is converted with a fixed ratio, so using it directly to judge how dry or wet the snow is will not be accurate.

Key point: first see which resort has deep snow, then how it changes by the day you arrive, and finally convert the precipitation.

After the forecast

In 西西’s words, once you have done this homework you can picture the state of the resort before you leave, and then decide whether to bring a powder board and how to plan your runs.

The last step is checking the resort’s own social media accounts. 西西’s example: Kamui Ski Links posts snow conditions on social media every day, down to how the snow feels to ride.

The post also gives examples of what a forecast cannot cover:

• On the ground: one day 西西 set out for Furano, then changed plans halfway and went to Katsurazawa instead. On that day, 15 January, a lot of the brush was still not covered by snow, and 西西 warned that care is needed outside the resort’s managed area.
• Regional differences: one year 西西 went to Asahidake on 30 November and said that from that day Asahidake was fully in deep-winter mode, while other areas were still only just holding on to their snow (the post does not give the year). Asahidake is not one of the resorts where SnowWind teaches.
• Timing: after six years of living in Hokkaido, 西西 says there are only a handful of powder days a year, which is why 西西 has never taken powder for granted.

The forecast tells you where the snow is. But the deeper the snow, the more homework you need to do.

西西

For that trip, 西西 also went and took AST Level 2 (avalanche skills training in the Canadian system). The trip included backcountry and sidecountry. The school’s position: backcountry riding is at your own risk, and you must go with a qualified local guide. For what an avalanche forecast can and cannot give you, see Can avalanches in Hokkaido be predicted?.

Powder inside the resort

This post is about picking a resort with good snow. Once you are at the resort, how to ride powder is covered in Riding Powder, Part 1; late-November, early-season snow conditions are in Part 2.

SnowWind lessons always take place inside the resort’s managed area, in terrain the resort permits and has open that day. To practise snowboarding in trees and powder, see the courses page; for powder data, see the powder data page.

Who this post is not for

• Anyone looking for a number like “once the snow is X cm deep, you can go into the backcountry”: this post does not have one, and should not.
• Anyone who wants to know that a given day will definitely be a powder day: a forecast can only help you picture it, not guarantee it.

The process and examples come from 西西's teaching notes; the original does not give the year for the Kamui Ski Links, Katsurazawa or Asahidake examples. This is 西西's personal process for choosing a resort, not a JSBA rule or official position. The original also included snow-liquid ratio conversions and snow-depth threshold figures; because there is no source we can check them against, this post does not use them.