Bollettino valanghe

Lutak

Haines Avalanche Center
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Pericolo valanghe

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

The avalanche danger is MODERATE at all elevations. Strong solar radiation at the snow surface causes wet loose avalanches and below 2,500ft prolonged above-freezing temperatures increase the likelihood of wet slab avalanches. Sunny aspects and lower elevations are most susceptible to warming. Areas of isothermal snow where you sink in deep along with roller balls and point releases are clues that surface layers are decreasing in stability.

Problemi valanghivi

  • Loose Wet

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

    Warming temperatures and strong solar radiation weaken the snow surface, making it possible to lose cohesion and slide down slopes.  Point releases can start small and entrain additional snow that is difficult to escape from and could push you into cliffs or trees; especially near cliffs and rocks and on slope angles greater than 35 degrees. The sun can also weaken cornices, making them prone to natural failure and human triggering. It is important to give cornices a wide distance for safety and to minimize the time we spend underneath them.

    Use timing to travel through terrain early in the morning or late in the day, and consider how long slopes have been baking in the sun. Where loose unconsolidated snow is present, be especially careful to identify any potential terrain traps, like gullies, ravines, and potential overhead hazards. Wet snow moves slowly but can be dense and heavy, making it challenging to dig through or provide air pockets in the case of a burial.  If you can feel the sun, the snow can feel it too; take time to assess the slopes you are traveling on or above you.

    If you're warm, the snow is warm. Aspect and time of day can be taken into account to manage wet loose slides. 

  • Wet Slabs

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

    The 3/16 avalanche cycle demonstrated that buried persistent weak layers were widespread on a variety of aspects and elevations. These weaknesses within the snowpack could still be present, especially where overnight temperatures never reached below freezing and warming during the day further weakened the snowpack. In this scenario, meltwater could be flowing through weak layers to produce a more unpredictable and hazardous wet slab avalanche problem. Multiple nights of solid re-freeze are required to reduce the likelihood.

    Wet avalanches can increase with intense warming and heavy precipitation, causing climax avalanche cycles. It will be important to consider these factors as we monitor future weather events, knowing that a variety of weak interfaces formed and were buried throughout the season. Another consideration is large natural triggers like cornice falls, or surface avalanches that could step down around shallow terrain features and produce persistent failures. Identify terrain where the problem exists and use extra wide safety margins to reduce exposure.

    Old crown and debris from 3/16 avalanche cycle on an NE-aspect at 4,000ft. Deeper layers are currently bridged by strong surfaces but could wake up with intense warming or precipitation. 

Avalanche Discussion

Notable layers in the snowpack:

  • Precipitation on 3/25-26 with freezing levels around 3,000ft
  • Light precipitation on 3/17 above 3,500ft and a calm extended period of high-pressure system.
  • Freezing levels spiked to 6,000ft on 3/16 which contributed to a widespread avalanche cycle.
  • 3-4" of SWE from 3/6-3/16 & wind loading from 3/14
  • Northerly outflow wind event- 50-100cm deep-Protected = preserved, near-surface facets or "recycled powder" formed in terrain protected from wind.-Extreme winds formed wind slabs that are now buried persistent layers.
  • Valentine's warm inversion, down 80-120cm: mix of melt-freeze crust, buried surface hoar, and hard sun-warmed surfaces.
  • The late January Pineapple Express crust. An intense precip event saw pooling and percolation with warming to 5,000ft.
  • End-of-Year Crust (EOY). Wet and warm end of last year, freezing levels to 4,000ft.

The people you go out with, how you communicate, and how you practice risk reduction as a team throughout the day are equally important as the conditions. Always practice 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. Carry radios, first-aid, and a two-way emergency communication device. Take an avalanche course, and practice companion rescue often with your riding group. Every scenario is different, so it pays to be prepared.

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

  • Avalanche Activity: Natural or human-triggered
  • Signs of Instability: Cracking, collapsing, or whumping
  • Red Flag Weather: Precipitation, wind loading, warming temperatures and rain-on-snow
  • Persistent Weak Layers: Surface hoar growth, snow depth, persistent weak layers, etc
  • Snow Pits: Stability test results, layers of concern, total snow depth, location, elevation, aspect, etc 

Were you caught, carried, injured, or buried in a slide? We can benefit from anonymous lessons learned. Please report incidents to Haines Avalanche Center staff confidentially.

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