Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Skiers and riders could trigger large avalanches 1.5 to 2.5 feet deep on weak snow above a crust at upper elevations. Slabs of wind drifted snow also also linger in the highest terrain. You may not see red flags like cracking, collapsing, and recent avalanches before triggering an avalanche yourself. You can use slope angle to avoid the problems entirely by sticking to slopes under 30 degrees. 

Problemi valanghivi

  • Persistent Slabs

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

    Large persistent slab avalanches are possible on upper elevation slopes. A slab of recent snow 1.5 to 2.5 feet deep rests on a weak layer of small facets above a crust on some upper elevation slopes. This was the weak layer in a large, widely propagating skier triggered avalanche in the Seeley Lake zone on Thursday. We also found the layer in the Central Bitterroot yesterday. 

    You may not experience signs of instability like collapsing or whumpfing before you trigger an avalanche on this layer. If you do see signs of instability, stick to lower angle slopes. You can identify the problem by digging in the snowpack and looking for a layer of weak snow just below the recent storm snow and above a stout crust. However, the weak structure may be difficult to identify because the faceted snow crystals are small. 

    There are also still areas with weak faceted snow buried near the ground. It has been over two weeks since the last avalanche on these deeper layers, but the poor snowpack structure remains. A persistent slab avalanche in the upper snowpack could step down and break out a deeper avalanche on one of these older layers. 

    You can use slope angle to avoid the problem completely by sticking to slopes under 30 degrees. Short of that, you can reduce your risk by avoiding large avalanche paths and those with ugly consequences if you are caught in a slide. 

    (2/15/2024)

    Aerial view of the avalanche that failed on facets above a crust in the Seeley Lake zone on 2/15/24.

  • Wind Slabs

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

    East winds this week drifted recent snow into wind slabs on west facing slopes and cross loaded terrain at upper elevations. The wind hit the Rattlesnake zone the hardest, but the highest elevations in all zones were affected. The wind slabs are becoming more stubborn, but they are still possible to trigger, especially in the highest terrain. 

    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.

    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

Avalanche Discussion

Today will be another excellent day for skiing and riding with beautiful weather and abundant recent snowfall. Over the last week, 1.5 to 2.5 feet of snow fell across the region. 

We have transitioned the storm slab avalanche problem to a persistent slab avalanche problem across the region. The recent snowfall rests on a layer of small facets above a crust on some upper elevation slopes. This means that the problem has not fully stabilized yet. We must remain cautious and shift to a persistent slab mindset to manage it. The close call on Thursday with a large, widely propagating persistent slab avalanche in the Seeley Lake zone reinforces this idea. The group reported that they did not experience any signs of instability before triggering the avalanche. They also dug a snowpit beforehand, and their extended column test was unreactive. 

The distribution of the persistent slab problem at upper elevations is still uncertain. All aspects at upper elevations are suspect until we can dial back the uncertainty. The simplest way to manage the problem is to stick to low angle slopes. 

Temperatures are cold this morning but will warm up by the afternoon under mostly sunny skies. Keep an eye out for small wet loose avalanches on steep south and west aspects today. Rollerballs and wet surface snow are signs to move to lower angle or shadier slopes. 

Let us know what you see out there this weekend by submitting an observation. Even reports of stable avalanche conditions are useful. 

Ski and ride safe. 

Regioni coperte