Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

6 to 10 inches of recent snow and moderate west winds built wind slabs on east aspects along upper elevation ridgelines. Skiers and riders could also trigger wet loose avalanches on sunny aspects today. A weak crust facet layer buried 1 to 2 feet deep further complicates backcountry travel today. Carefully evaluate the snowpack for unstable snowpit test results or signs of instability, such as shooting cracks or rollerballs, before committing to slopes over 35º. 

Problemi valanghivi

  • Wind Slabs

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

    Moderate west winds drifted 6 to 10 inches of recent snow into wind slabs on east aspects along upper elevation ridgelines. The Southern Bitterroot only received 2 inches of snow, so wind slabs are very small and isolated there. Wind slabs appear smooth and rounded and are often found just below ridges and in cross-loaded gullies. Cornices, wind lips, and drifts all indicate wind direction and loading. Signs of instability like shooting cracks warn you to stay off steep slopes. The best way to mitigate this problem is to avoid wind-loaded slopes over 35º. 

  • Loose Wet

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

    Small wet loose avalanches in the recent snow will become possible today on sunny aspects as they warm up under mostly clear skies. Increasing winds and high clouds this afternoon may limit the extent of solar warming. However, the recent snow is low-density and very susceptible to warming. In the Central Bitterroot, these avalanches could grow larger due to more abundant recent snow.  Elsewhere, they will be limited in size but could become large enough to push riders into or over terrain traps. If the snow is wet and rollerballs start, it's a sign to move to lower angle slopes or shadier aspects. 

  • Persistent Slabs

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

    A crust facet combo buried 1-2 ft deep has been found in isolated locations in the Bitterroot. Yesterday it was found on an upper elevation, southeast aspect in the Southern Bitterroot. Previously it was found on south, east, and north aspects at upper elevations throughout the zone. However, it is not everywhere, and many observations did not find the layer. Therefore, there is uncertainty regarding the spatial variability and sensitivity of this layer. It has produced propagating snowpit test results, but signs of instability have been isolated. It appears to be most sensitive in shallower areas at upper elevations, such as around wind-swept ridges.

    It is worth investigating the snowpack by digging a snowpit before you commit to steep terrain. Be prepared to change objectives if you find unstable results or signs of instability like whumpfing or cracking. 

Avalanche Discussion

Snow totals over the last few days are highly variable due to the showery nature of the snowfall. The Central Bitterroot received the most snow, with 8 to 10 inches. Totals in other areas range from 1 to 6 inches. The storm initially brought strong west winds, but they quickly died down as the snow piled up. The result is that sensitive wind slabs are isolated to near ridgetops in areas that received the most snow. Below ridgetops, there is excellent powder skiing in low density snow. 

In the southern Bitterroot yesterday, there was enough sun to cause a widespread rollerball cycle on south and west aspects. Further north, cloudier skies kept the snow cool. Today we can expect mostly sunny skies and light winds with increasing high clouds and winds in the afternoon. Small wet loose avalanches in the recent snow will become possible on sunny aspects. They will be the largest in areas with more abundant recent snowfall. 

The crust facet combo in the Bitterroot has been added as a new avalanche problem. It has been found sporadically throughout upper elevations in the Bitterroot zone, but the distribution is still unclear. It is worth digging down to see if it exists before committing to steep terrain. We will continue to track the layer as the season progresses. 

Stability is generally improving, and there will be excellent skiing and riding conditions today. However, in the last week, there have been several unintentionally triggered avalanches. Thankfully, everyone involved has avoided injury or burial. We still have a variable mid-winter snowpack with isolated weak layers. Remember that even a small avalanche can have serious consequences in unforgiving terrain. Do your homework before committing to steeper slopes, and use safe travel practices, such as riding one at a time. Low danger doesn’t mean no danger. 

Please let us know what you find out there by submitting an observation. 

Ski and ride safe.

Regioni coperte