Bulletin d’avalanche

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Haines Avalanche Center
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Danger d’avalanche

Alpin
1 · Faible
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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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 LOW at all elevations. A stable period of spring weather changes later today as wind, precipitation, and freezing levels rise late in the day into tonight. For now, hard surfaces from the past two weeks are present on all aspects making avalanche activity unlikely. As new snow falls or where old snow exists, areas of wind drifts could build at the surface, along with wet or loose snow.

Problèmes avalancheux

  • Storm Slabs

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

    Southeast winds are re-distributing any old snow available for transport and as new snow falls later today could form soft slabs over a variety of hard surfaces. Melt-freeze and sun crusts that developed during the extended period of sunny weather will be slick sliding surfaces. Expect slopes greater than 30 degrees below ridgelines and terrain features to be possible for human-triggering. In other areas, dependent on the elevation loose wet or dry snow may be sensitive where it is steep enough to slide. As accumulation picks up, consider the size of terrain features that could entrain snow and terrain traps such as gullies, cliffs, couloirs, or trees.

    Storm slabs can be wet or dry. They can present as wind slabs, or act as persistent slabs depending on where they form. Their formation will depend on the aspect and elevations. 

  • Persistent Slabs

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

    Hard surfaces continue to bridge deeper instabilities, however, the 3/16 avalanche cycle demonstrated that buried persistent weak layers were widespread on a variety of aspects and elevations. Lower elevations that did not experience a strong overnight freeze and upper elevations that were shaded from the sun could be locations more susceptible to the problem, even though human-triggering of these layers remains unlikely. This could change with warming temperatures or intense precipitation that breaks down the hard surfaces, especially near shallow areas in the snowpack like rocks, cliffs, and trees.  

    Old crown and debris from 3/16 avalanche cycle on an NE-aspect at 2,300ft. Deeper layers are currently bridged by strong surfaces but could wake up with intense warming or precipitation.

Avalanche Discussion

Notable layers in the snowpack:

  • 0.3" of SWE from 3/25-26 with freezing levels around 3,000ft.
  • 0.1" of SWE from 3/17 with freezing levels around 3,500ft then 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.

See full Seasonal Weather & Snowpack History here, or click the History tab

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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