Boletín de aludes

Lizard-Flathead

Mar 4 – 5, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Sat
Sun
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
4 · Fuerte
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Lo esencial

This is the first significant warm-up in March and we expect this to complicate current avalanche conditions. The danger may be CONDSIDERABLE in the morning but on the rise for the afternoon. Check out the new Forecaster Blog on warming and the effects on our complex snowpack 

Problemas de aludes

  • Cornices

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible - Likely
    Tamaño
    1–2

    Large looming cornices exist along ridgelines and require a wide berth from above and below. The likelihood of them becoming weak and failing is greater with warming and solar radiation. They have the potential to trigger slab avalanches from slopes below. 

    West to southwest wind has formed pockets of wind slab on leeward slopes. These could be triggered by the weight of a skier or rider, especially on east-northeast aspects. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2–3

    Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-50 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 60-100 cm. This layer consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. 

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Very Likely
    Tamaño
    1–2

    Wet loose avalanches are likely when the sun pokes out and freezing levels rise. Be observant as you travel, and look for signs of warming and snowpack instability. Snowballing, moist snow, and the most obvious is natural avalanche activity. Back off slopes and adjust your trip plan when things are heating up.

Confidence

Moderate - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather.

Weather Forecast

It's a hot and sunny forecast with generally light to moderate south wind. Thursday through Saturday will see mostly sunny skies with patches of cloud cover. Freezing levels are forecast to rise above 2000 m driving alpine temperatures above freezing. Sunday should bring cloud cover and a cooling trend. 

Avalanche Summary

No recent avalanche reports on Wednesday.

Sun and warming is our primary concern over the next few days. Large looming cornices may weaken and fail, triggering slabs on the slopes below. Loose-wet avalanches will likely be seen from solar aspects first and then possibly all aspects. The persistent slab sitting above weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers. 

Pockets of wind slab may be reactive on northeast-east aspects at upper elavtions. 

Snowpack Summary

Large, looming cornices exist on many ridgelines and threaten slopes below. Strong west-southwest winds have formed wind slabs on leeward slopes while freezing rain formed a widespread breakable crust 1-5 mm below 1800 m and in spotty locations at upper elevations. 

Up to 50 cm of snow sits above a variety of old interfaces that formed mid-February and 60-100 cm down is a persistent weak layer that was buried in late January. These mostly include sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. The South Rockies Field Team was near the powder cowboy sled zone today and their snowpack tests showed easy results (CTE 7 SC down 60) on a persistent weak layer.

There are no deeper layers of concern.

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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