Bollettino valanghe

Transitional

Haines Avalanche Center
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Pericolo valanghe

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

Light winds and cold temperatures have helped evade the immediate formation of a slab within the surface snow. Loose deposits are resting ontop of a widespread melt-freeze crust that formed up to 4,000' across all asepcts. Any wind effect could increase the liklihood of triggering a slide over this hard surface.

Problemi valanghivi

  • Loose Dry

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

    About 12-15" of loose and un-consolidated snow from January 3-4th has been preserved from well below freezing temperatures ontop of a 1" +/- thick "end of year" (EOY) melt-freeze crust. In this zone the EOY crust has been observed up to 4,000' on all aspects and that makes it a widespread bed surface. With the lack of significant wind, or warmer temperatures dry loose avalanches remain possible for human triggering on slopes greater than 35 degrees.

    Loose, non-cohesive snow can gain momentum and build into slides large enough to bury a human. Consider others hazards such as terrain traps like rocks, cliffs or trees that could increase the consequences of being caught in a slide, or where snow could pile up quickly

    Light winds could be variable with even moderate gusts being enough to form a more cohesive slab that would increase the liklihood of human triggering. Be on the look out for any recent signs of wind loading, or other red flags such as natural avalanches, cracking, collapsing/whumphing as loose snow consolidates or settles into a slab. Use caution around suspect terrain that could develop a slab, especially in exposed areas along ridgelines and in crossloaded gullies. 

Avalanche Discussion

As discussed in the dry loose avalanche problem above, any wind or settlement will increase the potential for a slab avalanche above the EOY crust. Weak angular snow grains known as facets are present above and below this crust and could increase propogation potential. Although triggering a slide below the crust remains unlikely, cold temperatures slow the healing process and drive faceting, or the weakening of these layers and that's what we have happening now. This can occur at a microscopic level due to temperature gradients being so small they are only detectible by infrared around a melt-freeze crust.

We should treat these layers as guilty until proven innocent and continue to monitor, track, and assess stability on a slope-by-slope basis. Melt-freeze crusts have played a role in avalanche accidents across our forecast zones and our state. Use safe travel techniques by only exposing one person to a slope at a time, avoid grouping up in run-out zones and re-consider islands of safety to truly limit your group's exposure. The people you go out with, the way you communicate, and the way you practice risk reduction as a team throughout the day is equally important as the conditions.

What we know about the EOY crust is that above freezing temperatures up to 4,000' due to an inversion at the end of the storm on Decemer 30th in the Transitional zone, caused the formation of a thick ( 1" +/-), widespread EOY melt-freeze crust.  The strength of this layer, thick and thiness is variable due to  duration and intensity of the EOY event and is elevation dependent due to a cooling trend that followed the increase in temperature at elevation.

Other layers to note are from earlier this season, and are now more than a meter deep. These include a few melt-freeze layers that are present throughout the snowpack at all elevations and aspects. These layers formed during other warming, or rain on-snow events and have mostly been found to be healing but could fail and produce a very unlikely though larger avalanche. Our overall warm and wet temperature regime through the season has helped slow the development of persistent weak layers (PWL's) in the snowpack. However at higher elevations and further inland these grain types can exist, and will require continued assessment. 

Help us gather information about weather, snowpack, and avalanche activity by reading and submitting field observations. Useful observations can be anonymous and include: 

  • Natural or human-triggered avalanche activity
  • Signs of instability: Cracking, collapsing, or whumphing
  • Red Flag Weather: Precipitation, wind loading, warming temperatures and rain-on-snow
  • Surface hoar growth, snow depth, persistent weak layers, etc
  • Snow stability tests, or pit result and location, elevation, aspect, etc 

Were you caught, carried, injured or buried in a slide? We are all human and can benefit from lessons learned, please report incidents to Haines Avalanche Center staff confidentially.

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