High cloud today with the sun poking through and cold temperatures with nice groomed runs this morning warming to plus zero temps now. No snow overnight but with no wind today it will be a nice one on the skifield. Yahoo are calling for more rain on firday though if it falls in the valley we can expect it to fall as decent snow at elevation. Also more snow on the radar beginning on the weekend.
SNOW STABILITY INFORMATION:
The early morning valley rain of January 19th soon turned to snow and proved to be a very good amount of snow at elevation. There was 45 cm at the top of Tsugaike gondola at 1500 metres and 30 cm at Goryu Alps Daira by the end of the storm. This storm snow has begun to settle and is bonding despite the two 10cm deep Grauple layers that are the only sign of weakness with in the new snow itself. This new consolidating slab is over riding the newly formed sun crust from Saturday’s strong solar radiation. Slope tests in the Tsugaike area between 1800 m and 2000 m during the JAN Avalanche Training School found that the new storm snow was sliding in ski cuts and hand tests on the solar exposed slopes. Wumphing associated with propagation over a large area was observed during a slope switch back cut test. The slope did not slide as it was a supported concave slope below tree line. This shows that larger wide open south facing steep convex slopes especially slopes that have scoured rocks and ridges or areas of shallow snow pack leading into steeper and deeper avalanche terrain.
Tests on more shaded aspects were not finding the weakness between the new storm snow and the previous snow fall as on the south slopes but there is still concern about the persisting instability around the December 23rd rain crust found to be down 120 ~ 200 cm. Deep Tap Tests resulted in hard‚ sudden planer fractures down 138 cm on mixed forms and facets overriding the rain crust @ 2000m on a north aspect in Tsugaike. This rain event was quite high in elevation and may still pose a greater Hazard in high alpine terrain on cross loaded‚ steep slopes and stay well away from unsupported slopes peppered with rocks at the surface or just below the snow surface. Take due CAUTION on all aspects in the Alpine such as terrain accessed from Happo or Goryu or even up high on the main Hakuba Ridge. Expect any avalanches coming down in the Alpine to be BIG and do not underestimate run out potential. (Those big South faces from Happo down to HiraKawa river valley are a prime and will decrease in stability with solar radiation and rising air temperatures) WATCH OUT CROSSING RUN OUT ZONES!
Northern aspects have not had the same solar radiation creating the same persistent instabilities as the south slopes. There is instability in the new storm snow and ski snowboard triggered slabs and sluffs in steep avalanche terrain are probable.
The sun crust of January 4th is still a possible concern especially on steep Alpine terrain on solar exposers and there is there is also the Dec 23rd rain crust that is still a concern as we receive more snow and today’s possible strong solar radiation puts extra stress on those lower layers.
The large size 3 avalanche on the south face of Happo that released in the early AM of January 14th‚ that traveled from the crown fracture beside Happo’s Grat Quad lift at 1600 meters right down to the first of the large concreate dams just short of Gentaro dam at 900 meters. The total length of the slide was over 1 kilometer and the deepest area along the Crown was 130cm and only about 20 cms at the flanks or side of the avalanche. Definitely the facets‚ around the rocks as well as above and below the Jan 4th sun crust‚ are the root of the reason for this large slide. The recent new snow and moderate North westerlies have continued to put increased weight on similar dense slabs that are over riding the January 4th sun crust.
Be extremely careful of entering into lee slopes from scoured ridges or convex terrain and around warming rock bands.
Areas of deep snow pack will have greater stability than the thin and areas where overnight radiation of heat has created near surface faceting and faceting crystals around the areas of shallow crust. Big alpine bowls may be slower to stabilize and may propagate very wide due to the very tensile nature the present wind effected alpine snow pack.
Continued caution around cornices should be practiced and these areas avoided all together. CORNICES ARE VERY FRAGILE!
Grauple layer under new snow
Surface avalanches in new snow due to underlying grauple layer
High density new snow over lower density snow layer
Increased snowfall adding load to buried week layer
Steadily increasing air temperature
Radiative cooling of snow surface causing low density snow and frost at surface
Falling tree bombs (Possible triggers and cause of avalanches as well as overhead hazards)
Solar radiated cornices becoming weak with direct solar radiation.
Use caution if crossing solar radiated slopes.
Increased caution advised around rocky outcroppings‚ cliffs and well spaced trees in start zones.
Development of cornices in lee slopes
Lee side loading
Windward scouring of ridges and rock out-crops creating uneven loading of slopes
Due caution on cross loaded slopes
Poor bonding at or around buried crust
Facet layer around buried crust
Wide propagation due to wind slab
Stay away from steep and convex terrain
Danger Level Updated at 2009 1/21(Wed) 6:00
Danger Level 3: Considerable
Natural avalanches possible. Human triggered avalanches probable
Danger level ratings are set for conditions at tree line
and may vary from below tree line and High Alpine areas.
Use this information as a guideline only.