Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Human triggered avalanches at upper elevations are likely today on buried persistent weak layers and wind slabs that formed in the past week. Mid elevation avalanches are possible, especially in areas where more snow fell in the last week, like Seeley Lake and the central Bitterroot.

Bitter cold temperatures will complicate any injury or gear problem and make a small avalanche or injury potentially life-threatening. 

If you encounter collapsing, cracking or see recent avalanches on slopes similar to what you plan to ski or ride, stick to slopes under 30 degrees in slope angle. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Human triggered persistent slab avalanches are likely today on middle and upper elevations. A variety of overlapping buried weak layers, including surface hoar, near surface facets, and depth hoar exist on all aspects at upper elevation and north through east aspects at mid elevation. Recent snowfall has stressed these weak layers to their breaking point and avalanches are likely today. It will be possible to remotely trigger an avalanche from above, below, or to the side of slopes. 

    You can recognize persistent weak layers by digging into the snowpack and looking for a dense slab on top of weak, sugary snow. Buried surface hoar can be more difficult to identify in a snowpit but often appear as a thin horizontal line across the snowpit wall face. 

    Red flags include wumpfing, collapsing, shooting cracks, and recent avalanches. If you encounter any of these or find a poor snowpack structure of buried weak layers below a slab, stick to slopes under 30 degrees.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Wind slabs are decreasing in sensitivity, but triggering a wind slab avalanche at the upper elevation is still possible. In the past 36 hours, non-typical east winds have built fresh wind slabs in atypical locations. Since January 7th, a layer cake of wind slabs has formed on all aspects. Periods of strong wind speeds built wind slabs lower on slopes than usual. These wind slabs may rest on persistent weak layers and act similarly to persistent slab avalanches. 

    Wind slabs are hard slab avalanches that often break above you and are very difficult to escape. Any wind slab also has the potential to step down onto deeper buried persistent weak layers, which can cause a large destructive avalanche. 

    How can you avoid wind slabs? Be suspicious of any slope that feels firm or has a hard slab on top of less cohesive snow. It may not always be obvious at first glance, as fresh snow will conceal older wind slabs. 

    Cracking, collapsing, or slopes with a smooth, rounded appearance are indicators of wind slab potential. If you encounter these, stick to slopes under 30 degrees.

Avalanche Discussion

It is time for a mindset shift as we exit a week of stormy weather and move into a period of no new snow. Peak storm instability, especially in the wind slab, has passed. We are moving into a period of dealing with multiple persistent weak layers and a snowpack with an overall poor structure. The good news is that this will heal with time. The bad news is that it takes time, patience, and the self-control to look at a tempting snow covered slope and not try to outsmart the avalanche problem to ski or ride it today. In times of extended considerable danger or persistent weak layer problems, it is human nature to push boundaries and start on a 30-degree slope, then a 33, then a 34, then... an avalanche. Resist the urge and enjoy excellent low angle skiing and riding until the snowpack strengthens. 

Temperatures across the forecast zone are nearing record lows, with overnight temperatures of -39 in the Seeley Zone as of 0400 this morning. In comparison, the southern Bitterroot seems tropical at just -18 degrees. These temperatures are dangerous and need to be respected. If you do travel in the mountains today, check out this blog from avalanche canada on managing extreme cold! 

Storm totals for our first significant winter storm (January 7th through 12th) are as follows:

North Fork Jocko SNOTEL (Seeley Lake): 13 inches with 1.7 inches of SWE ( snow water equivalent)

Stuart SNOTEL (Rattlesnake): 17 inches with 1.7 inches of SWE

Lolo Pass SNOTEL (Northern Bitterroot): 25 inches with 2.3 inches of SWE

Twin Lakes SNOTEL (Central Bitterroot): 37 inches with 4 inches of SWE

Saddle Mountain SNOTEL (Southern Bitterroot): 14 inches with 1.6 inches of SWE

The snowpack is slowly building on lower elevations. As much of the new snow fell on dirt, there are no persistent weak layers with a slab sitting on top. For this reason, low elevations are at a low danger for the day. Continue to keep an eye out for ground hazards such as downed logs, stumps, and rocks. They may exist under new snow and be obscured from view.

On January 11th, a skier passed away in an avalanche near Steven’s Peak, in Shoshone County, Idaho. We would like to extend our condolences to family and friends.

Let us know what you are seeing in the mountains by submitting an observation. Even just a photo or letting us know how much snow fell helps us greatly!

Stay warm and ski and ride safe!

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