Bollettino valanghe

Rattlesnake

West Central Montana Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Triggering an avalanche is likely today on wind loaded slopes. New snow and steady west winds have built wind slabs on upper elevation east aspects. 

If you see a smooth pillowy slab or experience cracking and collapsing, stick to slopes below 33 degrees. 

Sun and warm temperatures may cause wet snow avalanche activity this afternoon on south aspects.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Since Tuesday morning, 6 inches of low density snow has fallen in the Rattlesnake. This brings the new snow total for the week to 2 feet in the zone. Ridgetop winds have been steady out of the west in the moderate to strong category. The combination of new snow and wind has created wind slabs along east facing ridgelines. These slabs are sensitive, and human triggered avalanches are likely.  Watch for loading at convex breakovers, cross loading in gullies, or at cliff base. An avalanche in fresh wind slab also has the potential to release stubborn wind slab from last weekend, resulting in a larger, more dangerous avalanche.  

    Wind slabs can be identified by their smooth rounded appearance. Watch for shooting cracks, collapsing, or a hollow feeling slab. If you encounter any of these, stick to slopes under 33 degrees. 

    (2/1/2023)

    Shooting cracks at ridge top and the left flank of the resulting wind slab avalanche.

    Photo: Jeff Carty

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Today, skies will be clear, and temperatures could rise to the mid to upper 30s. Wet loose avalanches are possible on sunny aspects. 

    Watch for rollerballs or point releases off rocks and trees, as these are early indicators that conditions for a wet loose avalanche cycle are building. If you find yourself collapsing through unsupportive wet snow, stay out of avalanche terrain and pay attention to what is above you. 

Avalanche Discussion

Seeley Lake and the Rattlesnake have received the most snow in the past two days. In Seeley Lake, a foot of low density snow has fallen since Tuesday. As you move south through the Bitterroot, there is significantly less new snow. Winds, however, have been consistent through all zones, with ridgetop winds steady out of the west. Wind speeds have been ideal for transporting snow, especially the low density snow that fell in Seeley Lake. 

Wind slab is the primary concern today in all zones. Observers reported two feet of snow available for transport and a sensitive slab forming on east aspects. In Seeley Lake and the Rattlesnake, fresh wind slabs could be up to 3 feet deep and capable of avalanches D2 in size. Any fresh wind slabs are going to be sensitive, and human triggered avalanches are likely. Last weekend, we saw a significant natural avalanche cycle on wind slabs on all aspects. Triggering one of these old slabs is unlikely at this point. An avalanche on the new wind slab may have enough force to release an old slab, resulting in a larger avalanche. 

Clear skies and warm temperatures today may result in some wet snow avalanches. Often, when we see warming and sun on fresh snow, it leads to widespread but small wet loose avalanches. If you see indicators that the snow is getting wet or losing strength, stay out of avalanche terrain on affected aspects. 

We have removed the persistent slab concerns in Seeley and the Rattlesnake, as well as the deep persistent slab from the southern Bitterroot, from the problem descriptions. These layers are gaining strength and have been tested thoroughly over the past week without any reported avalanches. In the southern Bitterroot, there are still areas at upper elevation north aspects with weak basal facets. It is unlikely to trigger an avalanche on this layer but remains a low probability, high consequence problem.  In the Rattlesnake and Seeley Lake, any buried surface hoar was likely destroyed during the natural avalanche cycle in these zones last weekend. 

 

Please let us know what you are seeing today by submitting an observation.

Ski and ride safe. 

Regioni coperte