Bollettino valanghe

Continental

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Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

The avalanche hazard is Considerable above 4000 feet. Human triggered avalanches 1-3 feet in depth are likely in areas that have been loaded by north wind over the last 24 hours.  Watch for signs of unstable windslab such as shooting cracks and collapsing.  The hazard decreases with elevation and lower exposure to wind.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Outflow winds are expected to continue today before easing on Saturday as winds switch to south.  Wind strength is not expected to be as strong as yesterday.  If wind direction changes even slightly, slopes that were unaffected yesterday may become loaded.

    Sensitive wind slabs and small skier triggered avalanches were reported yesterday in the Maritime and Continental climate zone.   The same avalanche problem can be expected today, although the characteristics of the slab will likely have changed.

    Think of Wind slab as a general avalanche problem.  There are many differnt types of wind slabs,  these differences are important in being able to recognize/ anticipate the conditions and how to deal with them.

    Yesterday, wind slabs were just begining to form and presented as fairly soft and quite sensitive (the differnce in density hard over soft is more subtle).  During this stage slabs may be easier to recognize by visual texture rather than feel (pillowed and or rippled appearance).   Human triggered avalanches can be numerous but smaller in size depending upon terrain and slab depth.

    Over time wind slabs change, they will become stiffer and begin to have a hollow drum like feel.  At this point slabs will often become more stubborn to triggers, but will have wider propagations if initiated due to the increased density of the slab allowing for a more cohesive unit.

    After 36-48 hours wind slabs often become strong and unreactive as long as they are not resting on facets.  Where they overly facets wind slabs will remain reactive for longer.  This distinction can be difficult because it involves identifying grain type and spatial variability can complicate this process.

    Today expect for slabs to be stiifer and more stubborn to triggers.  Although, once initiated larger avalanches than yesterday would be the result.  The Continental zone will likely have higher sensitivity.  Faceting in the upper snowpack is more likely in these locations.  Pay attention to wind redistribution patterns.  Once you realize what aspects are loaded find out the depth of slabs and test their sensitivity.    It is recommended to avoid terrain traps and slopes steeper than 32° where wind slabs exist.

    Small Skier triggered wind slab that was reported 12/28. SW aspect ~4000', South Tiekel

Avalanche Discussion

The main concern today will be wind slabs that have been formed over the last 24 hours.  Watch for the presence of these wind slabs and avoid areas steeper than 32° where signs of instability are present like shooting cracks or collapsing.

The hazard is expected to be highest on the lee side of high elevation ridgelines.  At mid elevation crossloaded terrain is a concern and human triggered avalanches will be possible. At low elevation the effect of wind loaded snow is expected to be much less.  There is 4-8 inches of dry snow on a stout rain crust below 2000'.  The hazard will be low in these areas unless fresh wind slabs are present.

Overall better riding quality and stability will be found in wind protected areas.  The Christmas eve storm has been found to be well bonded.  Overall the snowpack currently has good strength and structure and instabilities should be concentrated near the surface and revolve around wind loading.

A layer of surface hoar has been reported to be forming in the continental zone.  Tracking the distribution of this layer will be important before the next storm rolls in.  Leave an observation if you notice the presence or lack of this layer forming.

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