Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
Open full map
Veraltet — dieser Lagebericht ist 6 months ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Today will be a beautiful spring day in the mountains. Don't let the blue skies fool you though, triggering a large avalanche on buried weak layers is still possible, especially on upper elevation north facing slopes. 

You may not see signs of instability like cracking or collapsing before triggering an avalanche. Dig in the snow and look for weak sugary snow with a slab above. If you find this, stick to slopes under 30 degrees in slope angle to avoid the problem. 

The safest and best quality riding will be on low-angle slopes sheltered from previous wind.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–3

    Most upper elevation slopes, and some mid elevation slopes, have at least one weak layer buried below a 1-3 foot slab. These layers have produced natural and human triggered avalanches over the last week with Seeley Lake producing the largest avalanches.

    The most dangerous slopes right now are at upper elevation north aspects where 2 distinct and reactive layers of surface hoar are buried. Surface hoar is a particularly nasty weak layer that can remain reactive long after it gets buried and is responsible for many avalanche accidents across the west. 

    As you move onto south facing or solar slopes, you will encounter buried facet/crust combinations. These layers have shown decreasing reactivity, but poor snowpack structure remains and snowpit test results still show potential for fracture propagation and avalanches.

    To identify the problem, dig in the snow. If you find a slab of firm snow on top of weak or sugary snow, avalanches are possible. Surface hoar will present as a thin grey line that runs across the snowpit wall. If you find this, be especially cautious as surface hoar can produce avalanches on slopes down to 30 degrees in slope ang

    You may not see any signs of instability like cracking, whumfing, or collapsing before you trigger an avalanche today. It will be possible to trigger avalanches remotely from below, above, or to the side of slopes. Just because you see tracks on a slope does not mean the slope is stable or incapable of producing an avalanche. In conditions like this, the 2nd, 3rd, or 10th rider on a slope can be the one to trigger the avalanche if they find the right trigger point.

    Photo: Cam Mackenzie

  • Wind Slabs

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

    Tuesday through Thursday, we saw large amounts of snow transported via wind with sensitive wind slabs. By today, there is less snow available for wind transport and new slab development is unlikely. These wind slabs are transitioning to more stubborn persistent slabs, and any avalanche triggered on them is likely to fail deeper on a persistent weak layer.

    If you do encounter fresh blowing snow, expect sensitive wind slabs in the area.  Wind slabs can be identified by their smooth and pillow like appearance or firm and hollow feeling. They often form downwind of ridges, rollovers, and gullies. 

    Avoid the problem by sticking to slopes less than 30 degrees. 

    Cracking in the surface snow with blowing snow visible behind. Both are signs that you should stay off of wind loaded slopes.

  • Loose Wet

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

    Today will be another unseasonably warm day with light wind and strong sun. Expect the snow surface to warm up fast on sunny slopes with a wet snow avalanche cycle possible. There are many factors that can affect the timing of a wet snow cycle, such as how much of a surface crust formed the day before and how long it will take that crust to break down before the snow can get wet. If you see rollerballs beginning to fan out and entrain snow into small wet loose avalanches, expect to trigger a larger wet loose avalanche if you enter avalanche terrain.

    If you find yourself sinking into wet and unsupportable snow, it is time to move to more sheltered terrain out of the sun to avoid avalanches. 

    There is a possibility of increased cloud cover this afternoon. If this high cloud cover arrives, wet snow avalanches will become less likely. 

Avalanche Discussion

The snowpack is in a transition period right now as we move from high danger and very reactive conditions, to danger trending downward and more stubborn avalanche conditions. 

Don’t be fooled though, there is still a 1-3 foot slab on top of weak snow. A common theme for avalanche accidents across the US is on clear sunny weekends following a storm. Lots of people are out in the mountains competing for fresh turns and before long, people are riding out onto slopes capable of producing avalanches. 

The last storm ended on the 25th and was followed by two days of strong wind. During this time we saw a natural slab avalanche cycle occur. This natural cycle is over, but it gives us a good indicator that the snowpack is stressed, and it won’t take much to overload buried weak layers and create an avalanche. 

If you get out in the snow, take a minute to let us know what you see. Your observations are a key component to an accurate avalanche forecast. Information about avalanches, the amount of new snow and wind, and riding conditions are all very helpful. Thanks in advance for your time, we appreciate you. Click here to access the observation submission page.

There has been a steady stream of avalanche accidents both fatal and non fatal in the past two weeks. Have fun this weekend, but ski and ride cautiously.

Abgedeckte Regionen