This personal blog contains snow, avalanche and weather data along with weekly commentary that may be useful in planning your Hakuba backcountry outings.

More important than anything else

1. Hakuba Avalanche Bulletin by the Japan Avalanche Network.
2. Understand the Avalanche Danger Scale.
3. Know what the avalanche problem is and how to avoid it.
4. Carry beacon, shovel and probe in the backcountry. Know how to use them.

Other useful info

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Recent weather data recorded at 6am each day for the preceding 24 hours. Altitude 800m.

Date Cloud Cover Precip type and rate Rain Altitude 6am temp Max temp Min temp 24hr New Snow 24hr New Water Equiv 24hr New Density Storm Total Snow Depth Baro Pressure
20180117 Obscured Rain - moderate 1400m?? 1C 7C 0C 0cm ~ ~ 0cm 125cm
20180116 Overcast Nil 1100m 0C 5C -2C 0cm ~ ~ 0cm 135cm
20180115 Clear Nil ~ -9C 0C -14C 0cm ~ ~ 0cm 145cm
20180114 Overcast S < 1cm/hr ~ -7C -4C -9C 29cm 23mm 90kg/m3 29cm 156cm

Hakuba Backcountry Weekly Snowpack Summary

13 January 2018

Welcome to the first snowpack summary for the season.

There is a rain crust from last week that extends to at least 2200m, maybe higher. I have not been higher. That crust is 15cm thick at 1900m. It is about 120cm deep at that elevation. It might become unstable as cold temperatures persist and facets grow around the crust, or the crust breaks down. Who knows. Bottom line: we have solid sliding surface and potential weak layer in our upper snowpack in mid January and that sucks a bit. A similar thing happened last season, with a terrible avalanche incident associated with it. I never trust crusts in the upper snowpack on steep terrain. Crust = more uncertainty. A snowpack comprised of ice crystals that fell from the sky, and nothing else, is the best type of snowpack. We had that. Now we don't.

BUT WHAT ABOUT THIS?....
In the alpine I have come to suspect, but been unable to confirm, the existence of a deep persistent weak layer in the form of basal facets associated with a crust. This is not common in Hakuba at all. Evidence:

- numerous slab avalanches with high crownwalls and wide propagation around 2500-2700m elevation on wind loaded aspect (east-something).
- our weather history at the start of the upper alpine seasonal snowpack accumulation: very short version... snowfall in the alpine in late October. Then 10 days of quite warm weather and rain to high elevation, with a few days of valley bottom temps between 15 and 20C. This would have created a crust. This was followed by an unusually cold second half of November and all December, which could have promoted the basal facet creation, with or without the crust.

This is pure speculation, based on circumstantial evidence and no time to visit the higher alpine to check the snowpack. I'm a busy guide, not a volunteer snowpack checker. I ski in the backcountry where my work takes me, and I share info that flows from those travels. If I am right about the basal facets, the kind of terrain where this might surprise you includes areas that are accessible, have not yet avalanched under natural load, and has thin snowpack areas for light-load triggering. Being unsupported would help. Candidates that come to mind: SE and N aspects of Norikura-dake. Korenge-dake. Karamatsu-dake. Kaerazu-no-ken. The steeps around the Vacuum. Shira-dake. Other places. If the basal weakness exists, it presents a very low probability but extremely high consequence human triggering event. More probable would be natural triggering from rapid intense storm loading, or high elevation warming (last week and sadly, also next week)

-damian, MountainLife Backcountry Guides, www.mountainlifebackcountry.com

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