Bulletin d’avalanche

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Haines Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
2 · Modéré
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 CONSIDERABLE above 2,500ft and MODERATE above 1,500ft. Northerly outflow winds have formed fresh wind slabs that will eventually become more stubborn to triggers as the event wears on. Look for blowing or drifting snow that will indicate recent slab formation. Factor this additional load over persistent layers into your terrain and route choice. Very cold temperatures and wind chill below -20F are other hazards to consider.

Problèmes avalancheux

  • Wind Slabs

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

    North and northwest winds with moderate to strong gusts continue to transport snow, forming slabs on slopes greater than 30 degrees. Be on high alert near summits, along ridgelines, cross-loaded gullies, and terrain traps. Look for visual clues, including natural avalanche activity and areas where winds have scoured slopes and then re-deposited onto loaded slopes.

    Winds could erode and weaken previously formed cornices and create new ones. We should give these a wide distance for safety and minimize our time near them.  Cornices are a good indicator that slopes below them have unstable snow and can be a large natural trigger for an avalanche, especially where persistent slabs (see Problem 2) are present.

    (2/29/2024)

    Winds transport snow at the Chilkat Pass as outflow winds continue to blow.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–2.5

    This period of cold weather will accelerate faceting on the surface and within the snowpack. Weak layers that can propagate from shallow to deeper areas include buried surface hoar, facets, melt-freeze layers, and depth hoar.  Signs of instability could be apparent, such as large whumphs and collapses, or non-existent.  A trigger like a cornice drop or wind slab could release deeper instabilities. 

    Remain suspect of unsupported slopes and shallow areas in the snowpack. Even smaller avalanches could be dangerous enough to have high consequences. Weak layers may be more or less apparent in certain areas, making mapping the problem tricky. Utilize cautious route-finding and minimize exposure by choosing safe spots to re-group and traveling one at a time. Travel where the snowpack is deep, consistent, and strong.

    (2/23/24)

    Old snow layers at Chilkat Pass 5-Mile Creek at 2,500ft SW aspect

Avalanche Discussion

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.

Recent weather history and snowpack layering:

  • Current - Feb 27th- Northerly outflow event with strong W-NW-N winds and cold temperatures. 
  • Feb 24th- Light snow through the region, with variable amounts of accumulation, 1-5". 
  •  Feb 17-21st - After the inversion broke down, temperatures rebounded right-side up with freezing levels reaching 2,500ft and a generally warmer temperature regime.
  • Feb. 13-16th - An inversion brought freezing levels as high as 7,000ft. Sunlight and melt-freeze weakened the new snow surface via recrystallization and surface hoar growth at and below the treeline.
  • Feb. 10-11th - Low pressure returned with strong southeast winds, increasing temperatures, and 1-1.5" of snow water equivalent (SWE). This storm produced a natural avalanche cycle on persistent weak layers.
  • Feb 7-8th - Cold temperatures and calm winds produced surface hoar and near surface faceting.
  • Feb 2-3rd - Light snow over our regions with the highest accumulations near town with 3-5".
  • Jan 31st-Feb 3rd - An intense northerly outflow event brought W-NW-N wind through the region. This was accompanied by another sharp drop in temperature with a maximum low of -15F at the Haines Pass. Another flip-flop weather event saw temperature increase between 25-40 degrees Fahrenheit.
  • January 27-29th - A two-pulse pineapple express event with ~6" total SWE. During the first wave, Jan 26-28th, 2-3" of SWE fell as temps climbed, with freezing levels peaking up to 5,000'. This was when a D3.5 slid over the Haines highway at 21 miles.  In part two of the event on Monday, Jan 29th, there was another 2-3"+ of SWE, but in 24 hours, it was colder with 2,500-3,000' freezing levels and moderate to gusting strong S-SE winds. These events helped create the current widespread melt-freeze surface crust nicknamed the late January Pineapple Express crust. 
  • January 2024 - 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. Three major temperature dips occurred around Jan 11th, Jan 19th, and Jan 22nd.
  • December 29th - The end of the year (EOY) melt-freeze crust is from when above-freezing temperatures  ~3,000ft- 4,000ft or higher caused the formation of a thick ( 1" +/-), widespread melt-freeze crust down 20-50cm. 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.

 

 

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 are all human and can benefit from anonymous lessons learned. Please report incidents to Haines Avalanche Center staff confidentially.

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