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
20180224 Clear S < 1cm/hr ~ -3C 3C -8C 2cm ~ ~ 2cm 171cm
20180223 Clear Nil ~ -4C 2C -6C 0cm ~ ~ 0cm 172cm
20180222 Overcast Nil ~ 1cm ~ ~ 5cm 179cm
20180221 Clear S < 1cm/hr ~ -3C 3C -3C 9cm 6mm 57kg/m3 9cm 182cm

180217 Hakuba Backcountry Snowpack Summary

If you ignore the unusual two rain events way back at the start of January, this season has been very good in the backcountry in and around Hakuba. Maybe not so great for people who come here to ski deep easy access powder on a regular basis. But great if you are a backcountry skier/splitboarder with a wider appreciation of good quality snow for extended periods (sometimes requiring driving and touring knowledge and effort to access). The next week looks like more of the same greatness which is nice to see as late Feb can be unreliable.

After rain on Sunday then a Siberian flow storm on Monday-Tuesday, the week ended with drier conditions and good backcountry skiing most days with a few small new snow top-ups, one bringing our first mild dust event from the Gobi Desert. There was some aging windslab, and a snowpack that had a lot of instability removed via a midweek avalanche cycle, and also 24 hour warm-cold temperature fluctuations into Friday. On top of that we are now getting a nice Siberian burst of cold snow over the weekend. This storm started cold and seems pretty straight forward. It is falling on what is probably a mostly good/normal upper snowpack and snow surface (from an avalanche perspective.) The coming days will see new storm slabs and new windslabs forming during and following the storm, then a period of colder settled weather that might once again give really good backcountry touring conditions. But always look out for rapid changes, like last week....

Lets recap what happened: the Siberian storm arrived, but was weaker than normal, maybe due to the westerly flow, and low winds unable to push over the Kita Alps to Hakuba. I don't really know. The storm accumulation started with an initial warm low pressure system (this was when it rained overnight at valley bottom on Sunday) before the colder Siberian system kicked in Sunday night. When it was raining at low elevation, a certain type of low density new snow layer was quietly accumulating above 1400m or so. That layer was about 5cm thick and is a known but not reliable weather event associated with low pressure systems (and rain). !!This situation was predicted as a possibility before it happened and documented in the JAN avalanche bulletin after it happened!! I could explain it, but have written it up so many times in the past that I can't be bothered doing it again. It all has to do with the different lift mechanisms producing the precipitation at the start and end of the storm accumulation (frontal v.s orographic.) Upper air temperatures also play a part.

So this storm had an observed and documented 5cm thick weak layer at the base of the storm accumulation, about 50-80cm total at 2000m. The storm fell with quite low wind. Notably in the Happo ridge backcountr, the wind was very low, which is unusual for that windy place during a storm. Lots of loose powder accumulated, and people where getting excited for a deep Happo ridge powder day when the storm ended. Then on Tuesday afternoon and night the wind suddenly picked up and all that deep loose storm snow was dramatically transported onto lee slopes in the form of windslab. That windslab took the accumulated storm layer (which was sitting on the low density weak layer) to tipping point and very quickly Size 2 and 3 and maybe even 3.5 avalanches started to run as the entire storm layer plus wind slab ripped out of steep terrain on the Happo ridge and ran with high destructive force to the rivers on either side of the ridge. This happened in numerous places, though to a lesser extent near Tsugaike. And it happened less so at higher elevation. This was a mid-elevation event, larger in the south of the valley, that ran into low elevation terrain. One significant avalanche started literally 400m from the top chairlift in Happo, in terrain that can be skied into directly off the lift with no effort or thought required. Someone died in that terrain last year. And someone else has been missing for a few days now on the Happo ridge. In the meantime, film crews and others were hanging around in the paths and run-outs of multiple large start zones during the day following this avalanche cycle.

-damian, MountainLife backcountry, www.mountainlifebackcountry.com

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