Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Small dry loose avalanches in new and recent snow are possible in steep, upper elevation terrain today. Recent loose snow avalanches and snow sluffing off your skis or sled indicate instability. Be prepared to manage sluffing and be aware of terrain where snow can concentrate and carry you into terrain traps and cliffs.

Although unlikely, you could still trigger a large persistent slab avalanche at upper elevations that fails on weak snow buried near the ground. You aren’t likely to see signs of instability such as cracking and collapsing. Dig down to look for poor snowpack structure (firmer snow sitting above weak, sugary snow). If you find poor structure and want to avoid the problem, stick to low angle slopes.

Problemi valanghivi

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Small human triggered dry loose avalanches are possible today at upper elevations. New and recent snow at the surface is soft and unconsolidated, and could slide off of steep terrain. Natural sluffing may occur in steep slopes with loose surface snow as well. 

    These avalanches will be larger on colder and shadier slopes where the snow has not settled as much and remains softer and drier. They will be smaller on warmer and sunnier slopes but could still be dangerous if you are caught and carried in consequential terrain.

    Utilize techniques to manage sluffing from your skis or sled. Minimize time spent in long-running gullies where avalanche debris will concentrate, or underneath steep terrain where sluffs can initiate from. Pay attention to hazards that a small avalanche could carry you over, such as exposed rocks and cliffs.

    (2/9/2024)

    Dry loose sluffing of new snow on a steep north facing 

    Photo: Payton Schiff

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    Although unlikely, skiers and sledders could still trigger a large persistent slab avalanche on upper elevation slopes. These avalanches could fail 2 to 4 feet deep on buried persistent weak layers near the ground. 

    The problem exists in isolated areas starting at 6500 ft and becomes more widespread as you get higher in elevation. North and east aspects have the most concerning snowpack structure, with a stiff slab above dry, weak, sugary facets near the ground. A poor snowpack structure also exists on south and west aspects where the facets are still wet from last week’s warm temperatures but continue propagating in snowpit tests. 

    The consequences of triggering a persistent slab avalanche remain high. You aren't likely to experience signs of instability like collapsing or cracking as you travel through the mountains. Previous tracks on a slope are not indicators of stability - avalanches may be triggered after many riders have negotiated a slope. 

    The best way to identify the problem is to dig down into the snowpack and look for poor structure with a firm slab sitting on top of weak, sugary snow. If you find this, individual risk tolerance will dictate how steep of a slope you are willing to expose yourself to. However, if you want to avoid the problem, stick to slopes less than 30 degrees. Short of that, you can reduce your risk by avoiding large avalanche paths that can carry you a long distance and those with big hazards that an avalanche could carry you over, such as exposed rocks and cliffs.

    (1/22/2024)

    Hard persistent slab avalanche from an avalanche accident on the Beaverhea

    Photo: Beaverhead FS

Avalanche Discussion

After a predominantly snowy week, conditions will be dry today and tonight, with a ridge of high pressure building over the forecast region. Temperatures will hover around 30 degrees F during the day, and a light wind will blow from the west. Temperatures will drop into the teens (F) overnight.

With about 1 foot of new snow, skiing and sledding conditions have improved within our forecast region. However, avalanches in this new and recent snow are today's primary concern. This snow sits on a hard melt freeze crust in many areas that may act as a slick sliding surface. Hazards such as cliffs or rocks that still exist under little snow could cause traumatic injury if you are carried over them. Don't be caught off guard by sluffs of dry loose snow, particularly in steep, shady terrain.

Isolated wind slabs may exist on or just below north and east facing ridgelines, or in cross loaded gullies at upper elevations. On Wednesday, a skier had a close call with a wind slab avalanche in the Bitterroot zone. This snow often looks rounded and pillowy. It will feel more dense and consolidated than surface snow that has not been wind affected. If you notice cracking or recent wind slab avalanches, avoid entering into steep terrain where wind affected snow exists.

Although decreasing in likelihood, the persistent slab problem remains a concern.  Observations continue to report poor snowpack structure and propagation in snowpit tests. Buried surface hoar still lingers, and continues to fail and propagate in snowpit tests as well. You are most likely to trigger a persistent slab avalanche in areas with shallower snowpacks, and these avalanches will be most consequential in high, north and east facing terrain. It should be noted that we found a much more well-bonded snowpack on the west side of the Seeley Lake zone this week. The facets near the ground had rounded and gained significant strength. The higher snowfall amounts in this part of the zone have contributed to the healing process.

The persistent slab problem is a low likelihood, high consequence scenario. Choosing to enter avalanche terrain is a matter of personal and group risk tolerance. Use safe travel practices, such as riding one at a time, regrouping in protected areas, and spreading out on a slope. Facilitate clear communication with your group members and respect any vetoes that arise. If you find poor snowpack structure and want to avoid the problem entirely, stick to slopes less than 30 degrees. 

Our intern at the avalanche center is conducting graduate research on avalanche forecast usage. Data from this research will help the avalanche center learn how to better serve the backcountry community in west central Montana. Please consider taking a few minutes to fill out the survey.

Ski and sled safe!

Regioni coperte