Boletín de aludes

Seeley Lake

West Central Montana Avalanche Center
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Peligro de aludes

Sun
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Human triggered avalanches large enough to bury, injure, or kill a person are likely on the eastern side of the Seeley zone in the southern Swans. These may be triggered from above, below, and to the side. Leave a wide margin of safety between you and avalanche slopes over 30º. In the southern Missions, persistent avalanches are possible. Avoid slopes over 35º and steer clear of thin areas near rollovers and start zones.

Problemas de aludes

  • Persistent Slabs

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

    The persistent avalanche problem hazard divides the Seeley Lake zone down the middle. 

    The eastern portion in the southern Swans has a much shallower snowpack, close to half the amount of the southern Missions. As a result, the snowpack is faceted and weak, with a very poor structure. You are likely to trigger avalanches large enough to bury, injure or kill a person in upper elevation terrain over 30º in the southern Swans. All observations from the southern Swans in the past week indicate touchy conditions; widespread collapses were reported at Morrel on Thursday. Avalanches in this zone could be triggered remotely from above, below, and to the side. Leave a wide buffer between yourself and avalanche terrain. 

    The southern Missions have a deep and bonding snowpack. Pockets of persistent slab remain, but they are deeply buried and stubborn. It is possible to trigger these on northerly and shaded aspects where the October snow was preserved. Avoid shallow, windswept start zones around rollovers and ridges, and slopes over 35º.

    Unstable conditions could be found throughout the zone. Soft sugary snow, punching to ground when you step off your machine or skis, whumpfing and cracking are all indications of a weak snowpack and unstable conditions. Step back to mellower terrain if any of these are found.

     

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–1.5

    Winds have been westerly and moderate, with strong gusts. Easterly slopes have been loaded, and wind slab can be triggered at upper elevations below ridges and along the edges of cross loaded gullies. 

    Wind lips and cornices indicate wind direction and loading. Pay attention to the snow and avoid hollow sounding pillows, drifts, and wind loaded start zones over 35 degrees. 

    In the southern Swans, wind slab may trigger deeper persistent weak layers, avoid slopes over 30º in this area.

     

Avalanche Discussion

In the past 48 hours, the mountains have received between 2” and 4” new snow. Winds have been moderate and westerly with strong gusts. Temperatures have been in the mid teens. Today a trace of snow is forecast. Winds will be moderate out of the southwest, and temperatures will be in the mid 20s.

The past week has been relatively mild compared to the week before. Some snow trickled in, a few inches here and a few inches there. Not enough to tip the balance on the weak layers present. The temperatures have been moderate, not warm enough to significantly bond the facets in the snowpack, and not cold enough to make them much worse. Conditions remain similar to the previous two forecasts, challenging and sketchy. 

Drastic differences in snowpack depth, coverage, and weak layer distribution mean varied hazard in each zone and necessitate careful attention to conditions. In many places in our forecast area, the snowpack structure is very poor; in these places, human triggered avalanches are likely. The problem is widespread enough to keep the hazard at considerable. Generally, areas where the snowpack is under 4 feet deep have touchier persistent weak layers, and the likelihood of triggering slides is higher.

The poor structure alone in these areas should be enough to keep you off any avalanche slopes. Collapsing and cracking are further signs of instability. These warning signs have decreased as the overlying slab has stiffened, but the potential for larger avalanches has increased. Stability tests are redundant when poor structure and signs of instability are present. If you use the extended column test to check stability, don’t trust a lack of propagation as a sign of stability, the current persistent problem can produce false stable results. Take any propagation that does happen as extra confirmation to stay out of avalanche terrain.

Certain areas, such as the southern Missions and the central Bitterroots around Lost Horse and Camas Lake, have a deeper snowpack, and weak layers have bonded. As a result, avalanches are less likely. However, careful assessment is still required. If you are in doubt about stability, the easiest approach is to manage terrain and stick to slopes under 30º. 

Remember to check the forecast zone you plan to ride, sled or ski in, as there is information specific to each zone. 

Submitting an observation doesn’t require special training or knowledge, and our new observation platform makes it easier than ever. Please let us know what you are finding out there. 

Ski and ride safe. 

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