Bollettino valanghe

Chilkat Pass

Haines Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

The avalanche danger is CONSIDERABLE above 1,500ft. Strong northerly winds continue to re-distribute snow and build wind slabs at mid-to-upper elevations. Look for old and new signs of wind-loaded slopes in any terrain greater than 30 degrees including run-out zones below. Frigid temperatures and hard refrozen snow surfaces are other current hazards.

Problemi valanghivi

  • Wind Slabs

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

    Look for visible transport of snow and avoid terrain where wind slabs have been built up on slopes greater than 30 degrees. Northerly winds have been blowing snow from one aspect to another mostly loading E-SE-S aspects, however, expect to find them in all terrain.

    Shooting cracks, collapsing, and areas of more cohesive snow formed by the wind are indicators you are on a wind slab. With how strong the winds are wind slabs can form well below a peak or ridge down the slope and at mid-elevations.

    Use careful terrain identification to bypass slopes that could slide and areas where you could trigger a slide from below. Give yourself wide margins for error if you are traveling around wind slabs.

    Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–3

    We should treat buried weak layers as guilty until proven innocent, which involves slope-to-slope assessment. After a natural avalanche cycle last weekend, it is uncertain what buried weak layers failed and whether or not they were wiped out. The possibility exists that some have survived, particularly at higher elevations, further inland, or up in glacial valleys where the air may have been colder. Or even weak layers that failed and have since been re-loaded with new snow. A high degree of uncertainty requires, again, wide margins.

    Known buried persistent weak layers included melt-freeze faceted layers, buried surface hoar, buried near-surface facets, and depth hoar. South winds were visibly transporting snow on top of north aspects earlier in the week and could have buried the "January Pineapple Express" (JPE) melt-freeze crust that developed when freezing levels increased to 3,500-4,500ft. '

    Keep in mind that persistent slabs have the potential to propagate an avalanche from a thin area of snow to a deeper one that fails on buried weak layers across the terrain. Avoid high-consequence run-out zones and terrain traps.

     

    (2/1/2024)

    Crowns lines on an NE-Aspect of Three Guardsman at 5,600'. It is difficult to know whether this failure occurred more recently, or this past Sunday when temperatures rose. New snow may have re-loaded over old buried persistent weak layers. 

Avalanche Discussion

Last weekend, we got walloped by a two-pulse late "January pineapple express" event with ~6" total SWE (snow water equivalent.) During the first wave, Jan 26-28th, 2-3" snow water equivalent (SWE) fell as temps climbed, with freezing levels peaking up to 5,000'.  In part two of the event on Monday, Jan 29th, there was another 2-3"+ of SWE, but in 24 hours, and colder with 2,500-3,000' freezing levels and moderate to gusting strong S-SE winds.

Above-freezing temperatures spiked on Sunday, Jan 28th, in the evening, where some slopes had avalanches occur on persistent layers- including the large, D3.5-sized avalanche at the 21-mile Haines Highway. When the weather picked up again on Monday, strong winds and snow above 2,500-3,000' covered and reloaded start zones. This blend of events makes mapping the distribution of avalanches difficult, bringing uncertainty to where persistent layers remain. 

Other layers to note are from earlier this season: faceting from cold, northerly outflows, and melt-freeze layers throughout the snowpack.

  • Cold temperatures most of January faceted and accelerated the weakening of persistent snow grains throughout the snowpack: at the surface, below wind slabs, near melt-freeze crusts, and on the ground, especially in areas with a shallow snowpack. 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.
  • The melt-freeze crust of most concern is the EOY (End Of Year crust.) What we know about the EOY crust is that above-freezing temperatures  ~3,000ft- 4,000ft 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 depend on the duration and intensity of the warm and inverted EOY event. The cold weather in mid-January faceted and weakened snow around the crust. The "late-January pineapple express" had avalanches that released EOY instabilities in some areas but inconclusive in others.

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. 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. 

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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