Boletín de aludes

Rattlesnake

West Central Montana Avalanche Center
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Peligro de aludes

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

Lo esencial

1-2 feet of snow has fallen during the past few days, and human-triggered avalanches are possible. Today should be excellent for skiing and riding, but don't let the powder cloud your judgment.

Watch for red flags like shooting cracks and recent avalanches. If you encounter these, step back to slopes under 30 degrees in slope angle. Storm snow instability is short lived, and by tomorrow, much of the instability will have passed.

Problemas de aludes

  • Wind Slabs

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

    For the past 36 hours, sustained east wind has built fresh wind slabs on west facing slopes and cross loaded complex terrain. Yesterday, these slabs were reactive and forecasters could trigger small pockets of wind slab at upper elevation. These wind slabs will continue to be sensitive today, and human triggered avalanches are possible.  

     Wind slabs often form along ridgelines, in gullies, around rocks, and on convex rollovers. East winds are not the normal wind direction and you will likely encounter wind loading in terrain opposite where you usually find it in the Rattlesnake.

    Wind slabs can often be identified by their smooth, rounded appearance. If the snow feels hollow under you, this is also a good indicator of wind slab. Avoid the problem by sticking to sheltered or wind scoured areas.  If you encounter sensitive wind slabs or are seeing red flags like cracking and collapsing, stick to slopes under 30 degrees.

    (2/15/2024)

    Small intentionally triggered wind slab on an upper elevation west aspect. 

    Photo: Arden Feldman

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2.5

    Triggering a large persistent slab avalanche at upper elevation is a low likelihood, high-consequence scenario. It has been two weeks since the last avalanche on these layers, but the poor snowpack structure remains with a slab over weak, sugary snow.

    Dealing with this problem is an individual risk tolerance question.  Use slope angle if you want to avoid the problem completely by sticking to slopes under 30 degrees.

Avalanche Discussion

Today is looking to be an excellent day for skiing and riding. Winds will decrease throughout the day today, and skies will be clear by evening. 

New snow since the 11th

Seeley Lake NF Jocko: 17 inches

Rattlesnake Stuart: 9 inches 

Bitterroot Lolo Pass: 9 inches

Bitterroot Twin Lakes: 7 inches 

Bitterroot Saddle Mountain: 10 inches

Our weather stations are few and far between, and SNOTEL data and field observations have not lined up well. Weather stations sometimes reported just a few inches, while field observations reported a foot or more of new snow. If you are in the field and noticing conditions different from what was forecasted or reported, please let us know. It helps fill the gaps where we have missing or incorrect weather data. 

Instability from this storm will be short lived. If you encounter red flags or avalanches today, step back and try again tomorrow. There is a good chance that much of the storm snow instability will have settled in that time. 

Except for the Rattlesnake, most of our forecast zones were sheltered from strong east winds the past few days and as a result, wind slab is the primary problem in the Rattlesnake. That does not mean other areas didn't get clipped by some east winds, particularly along the Swan crest, where isolated wind slabs could be lingering.

What about the persistent slab problem? Why is it still on the forecast if it is unlikely? Even though we have not seen an avalanche on these deeper facets in two weeks, we are still uncomfortable with the poor snowpack structure and the potential for a large avalanche to surprise someone. How much you are willing to expose yourself to this problem is a matter of personal risk tolerance. Be aware that any avalanche triggered near the ground will be large and potentially catastrophic. 

Let us know what you are seeing by submitting an observation.

Ski and ride safe.

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