Lawinenlagebericht

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Haines Avalanche Center
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Lawinengefahr

Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

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.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Look for visible snow transport 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 where human triggering is likely.

    Shooting cracks, collapsing, and areas of more cohesive snow formed by the wind are indicators you are on a wind slab. With the strong winds, 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 a wide margin for error around wind slabs that could step down to persistent layers (see Problem 2).

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

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    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)

    Faint crown lines on NE-aspect of Old Faithful Mountain at 4,200'. 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'.  Part two of the event on Monday, Jan 29th, was about the same 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.

Cold temperatures most of January 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  ~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 has released deeper instabilities in some areas and inconclusive in others.

Other layers to note are from earlier this season, including a few melt-freeze layers present throughout the snowpack formed during other warming or rain-on-snow events.

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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