Bulletin d’avalanche

Lutak

Haines Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The avalanche danger is CONSIDERABLE between 1,500-3,500 feet and MODERATE  elsewhere. Wet snow avalanches are possible during the heat of the day in solar-affected southern aspects greater than 30 degrees.  In the wrong terrain, such as cliffs or a terrain trap, smaller slides could be consequential. Lots of folks are recreating this week; be considerate and aware of run-outs, your group, and other parties. 

Problèmes avalancheux

  • Loose Wet

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

    Warming temperatures and solar effect weaken the snow surface, making it possible for it 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; they are especially prone near rocks. How far you sink into the snow can tell you how warm the surface is and how close you could be to affecting a weak layer.

    The sun can stress cornices, making them prone to natural failure and human triggering. We should give these a wide distance for safety and minimize our time near them.

    Poor structure is present throughout the snowpack (see Problems 2 and 3), and although overnight freezing decreases the likelihood to unlikely-very unlikely, it is not impossible for them to get triggered- especially from the stress of a surface slide or cornice fall stepping down to the unstable layers below. 

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

  • Persistent Slabs

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

    Weaknesses within the snowpack are still present.  A significant slab has formed over an old snow surface from the extended cold period of northerly outflow winds. There is 3-4"+ of snow water equivalent (SWE) loaded over that weak snow interface. There was a significant slide cycle March 13-16th on these persistent layers about 1m deep. Most of these slides broke in steep terrain near/from rocks and cliffs.The cold, freezing nights will lock these layers up, making them dormant and unlikely to trigger.  They are within the snowpack; we need to factor in the unlikely but deadly nature of these slides and still practice good group management with safety zones and base camps.

    On the surface, areas of soft snow in higher elevations may have formed wind slabs from the N and NW winds. Trending to stubborn, use visual clues to identify and avoid wind-affected terrain and slabs. 

    (3/10/2024)

    A consolidated slab of new snow sits over the soft and weak old snow surface that failed with propagation. 2,500' N-Aspect ECTP26 down 70cm.

    Photo: Jeff Moskowitz

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–4

    While solid refreezing overnight should put these layers back to bed, we need to be aware of them- and not underestimate them. These widespread melt-freeze layers formed during warm weather events have now been buried 4-8 feet deep. A big trigger like a surface avalanche or cornice fall could step down into these deeper layers, causing a failure to propagate across multiple features. When thinking about safe zones, avoid avalanche run-out zones and consider the distance a slide could run with wide margins. 

    (3/6/2024)

    Notable deep persistent weak layers include the End of Year (EOY) crust visible below the pencil that still has faceted snow around the crust. See the forecast discussion and seasonal weather history tab for more information.

    Photo: Haines Avalanche Center

Avalanche Discussion

Notable layers in the snowpack:

  • Freezing levels spiked to 6,000ft, St. Patricks Day
  • 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.

  Early-mid March has historically come with avalanche accidents in our valley. As part of your trip plan, establish a mindset for your group before you venture into the mountains. This can help combat human factor bias and heuristic traps. Use weather, avalanche, and terrain checklists. Deploy ALPTruth:  

The ALPTRUTH acronym covers 7 contributory factors to avalanche accidents.  When reviewing over 1000 avalanche accidents, Ian McCammon found that 3 or more of these factors were present in over 90% of accidents.

  • A: Avalanche. Have there been any recent avalanches (within the last 48 hours)?
  • L: Loading. Has snow, wind, or rain loaded the slope in the last 48 hours?
  • P: Path. Will your planned travel path cross an obvious avalanche path? Will your uphill travel cross any potential avalanche paths?
  • T: Terrain trap. Is there a terrain trap? These include gullies, trees, cliffs, or other features. A slide into a terrain trap will increase the severity.
  • R: Rating. What does today’s avalanche report look like for your area? If there’s a rating of “considerable” or higher, you may want to reconsider.
  • U: Unstable snow. Have you heard any cracking, collapsing, whoomping? These are clear signs of instability.
  • TH: Thaw. Has there been recent warming of the snow’s surface due to sun, rain, or air temperature? Warming can increase instability and avalanche risk.

Thinking ahead:

  • When the next loading event happens, is it slow and incremental or rapid and significant?
  • What are the temperatures, steady and moderate, spring diurnal, or are freezing levels rising?
  • How does the likelihood of propagation increase or decrease with strength vs. structure?
  • Is there weak snow above or below a crust? How strong or brittle is the crust? Does the crust laminate well to layers above/below or not?
  • Could strong solar radiation or warming temperatures contribute to instabilities, including cornice fall?

Click here for a detailed season weather & snowpack history.

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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