Bulletin d’avalanche

Lutak

Haines Avalanche Center
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Danger d’avalanche

Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The avalanche danger is HIGH at all elevations. Increasing temperatures, strong winds, heavy precipitation, and rain on snow are all adding stress to buried weak layers. Wet-loose avalanches at low-mid elevations and storm slabs at upper elevations are very likely for human triggering today. Due to the potential for avalanches to step-down, avoid avalanche terrain including overhead hazards and run-out zones.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–3

    Smaller more likely avalanches from wet loose (see problem 2) or storm slabs (see problem 3) could add stress to buried weak layers and step down to cause a larger and deadly persistent slab avalanche. Expect a natural avalanche cycle to occur as temperatures rise throughout the day combined with heavy precipitation, strong winds, and rain on snow. 

    There are numerous buried persistent weak layers within the snowpack that prior cold temperatures have made worse. Slopes greater than 30 degrees have the potential to propagate an avalanche from a thin area of snow to a deeper one that fails on buried weak layers across terrain. 

    Hazards such as terrain traps like rocks, cliffs, trees, gullies, and road cuts increase the consequences of being caught in a slide, or where snow could pile up quickly. The possibility of an avalanche stepping down is a solid reason to avoid avalanche terrain all together at this time.

    (1/19/2024)

    Poor structure in a snow pit at 2,400' on a N-aspect in the Lutak Zone that includes the EOY crust now buried over 3ft deep.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–2

    Wet loose slides are very likely in low-mid elevation bands with rain on snow and could be large enough to bury a person. Be aware of rising freezing levels, and other signs like snow shedding from trees, rollerballs, and gloppy wet snow. Wet avalanches are difficult to escape and will be consequential in terrain that funnels you into trees, rocks, or onto a flat surface where debris piles up deep.  These surface slides could step down to persistent slab layers (see problem 1).

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–2

    In the upper elevations, storm snow is loading slopes and increasing the avalanche danger. Avoid steep slopes above 30 degrees, terrain traps, and run-outs. Southeast winds will be moderate, gusting strong together with heavy precipitation are forming increasingly touchy storm slabs. Signs of instability include cracking, collapsing, hollowness, and cohesive surface snow. These surface slides could step down to persistent slab layers (see problem 1).

Avalanche Discussion

Warming temperatures, increasing freezing levels, heavy precipiation, strong winds and rain-on-snow will all play a role to increase the avalanche hazard this weekend and into next week. Across all our forecast zones, on all aspect and elevations are buried persistent weak layers that could become more stressed and lead to an increased likelihood of human triggering along with a natural avalanche cycle, including roof avalanches.

Sustained north winds this past week have created thick and thin areas of the snowpack. This spatial variability results in certain shallower areas being where you could still trigger a slide from as it propagates into deeper areas. The winds may have also drifted snow further downslope and created pockets that are susceptible to mid-slope releases.

Freezing cold temperatures accelerated the weakening of snow grains throughout the snowpack: at the surface, below wind slabs, and above and below melt-freeze crusts. 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 are a dangerous weakness in a snowpack and have played a role in multiple avalanche accidents, even within our forecast zones.

What we know about the EOY crust is that above-freezing temperatures at all elevations on December 30th caused the formation of a thick ( 1" +/-), widespread melt-freeze crust down 20-50cm. The strength of this layer and its thick and thin variability is dependent on the duration and intensity of the warm and inverted EOY event. Very weak faceted grains have been observed around the EOY crust, and the cold is making them worse. 

Other layers to note are from earlier this season including a few melt-freeze layers that are present throughout the snowpack formed during other warming, or rain-on-snow events. Recent observations have confirmed a noteworthy December 24th Christmas Eve crust located down 60-90cm from when freezing temperatures reached ~3,000ft.  Periods of intense cold have not only weakened snow grains throughout the pack but have created NSFs. Jan 6-7, now up to two feet deep has been currently showing some reactivity on isolated wind-loaded aspects. A freezing drizzle left an ice lens about .5cm in the Lutak area on Sunday, Jan 14th. 

The wide propagation and dangerous nature of persistent slabs are best mitigated with safe travel techniques and terrain management- 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 are equally important as the conditions.

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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