This is my first weekly conditions report for the season.
Besides summarising, I won't repeat anything that is already available in the above sources of info. Please read them, especially the avalanche bulletin. Seriously, if you are not reading the avalanche bulletin, then don't bother reading this either. To be fair, the JAN avalanche bulletin has not started for the season. Hopefully it will start very soon, and when it does.... please do read it carefully. It is a vital resource and significantly, the Japan Avalanche Network was recently presented with an award for their service by the Federal Government. Don't let their hard work go to waste. It is your starting point for all backcountry trips :)
The last week:
A week ago there was moderate rain to below treeline, this quickly turned into a significant winter storm, with a pause, then another very short warmer afternoon where rain threatened, but none fell, it just snowed. Again, that turned into an even bigger, windier winter storm. In the last week, the daily 24 hour snowfall totals are: 3cm, 29cm, 65cm, 10cm, 9cm, 58cm, 67cm. Take a look at the seasonal comparison charts at the end of this article to see how unusual this rate of mid December snowfall is. There was obviously some very good skiing all week, with a brief moment to ski in the higher alpine earlier in the week where powder sat around without much wind influence at high altitude, particularly at the north end of the valley. There was not much direct evidence of avalanches reported due to the very limited visibility and the lack of people out there in the terrain. A Japan Avalanche Network member reported long shooting cracks and a Size 2 natural avalanche at the south end of the valley.
As of now, the 18th, it is snowing lightly as this last storm finishes, with strong winds easing, and the sun starting to break through. It is likely to have produced a denser cohesive slab sitting over lower density less cohesive snow, leading to a possible avalanche problem for a few days after the storm. Observations are required to confirm this. Right now, we don't know much. We do know that perhaps 200cm was loaded into treeline and the alpine, with a lot of wind. Common sense says that this is a time to step back risk taking until you know more.
The next few days:
Another low pressure system is building in the Sea of Japan, and again it will create a warm southerly flow with rain likely on Saturday evening to perhaps 1400m. However, this might change. Friday will be a lot clearer, raising peoples "feel good" vibe. Remember that blue skies and calm weather frequently leads to higher risk taking, even if there is an obvious avalanche problem. Try to keep that under control, especially on sunny aspects which are seeing the sun for the first time in days. Stability may react poorly to that on steep terrain. Saturday will be warm and turning overcast. Previously cold rapidly loaded snow seldom likes being warmed and lower altitudes may be quite unstable as the freezing level climbs towards treeline. Be very careful of that. Following the warm burst on Saturday, another colder flow will return with snow into Monday.
Have fun, every time you ski. Plan your backcountry trips in advance, choose good partners, all carry the required avalanche rescue and emergency equipment, tell some where you are going, and, if in doubt on a steep slope... don't do it. Remember to actively apply what you were taught in your avalanche courses. That training is useless otherwise. And have fun.