Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

On the north side of the compass, old hard slabs remain a low likelihood, high-consequence threat.  Persistent slabs are most likely triggered where the snowpack is thinner, often near rocky areas, convexities, or in wind affected terrain.  You can find a trustworthy snowpack with good stability during the early hours of the day on the south side of the compass.  As the snowpack heats up, the threat of wet avalanches will increase, including the isolated potential for a large wet slab.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–2.5

    Old, hard slabs 2–3+ feet thick linger over buried weak layers but are becoming increasingly stubborn to trigger and less common. Without obvious warning signs, avalanches are most likely triggered where the slab is thinner and easier to impact the weak layer below. The most fragile layers are buried in the middle and lower portions of the snowpack on northerly aspects. Persistent slab avalanches are dangerous in size; they can propagate widely and be remotely triggered from adjacent low-angle terrain.  The most reliable way to manage this problem is to choose conservative slope angles or travel on southerly aspects, where the snowpack structure has become stronger and more spring-like. On northerly aspects, avoid steep terrain with a thin or variable snowpack, such as rocky areas, rollovers, or places where winds have created uneven slab thickness.

    In the Northwest Mountains, our most recent persistent slab activity occurred during the last week of February, including this pair of destructive slabs.  

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    Time your travel early in steep, sunbaked terrain to avoid wet avalanches. Small wet loose avalanches are possible in very steep terrain, and there is isolated potential to trigger a much larger wet slab where meltwater drains into buried weak layers.  The most concerning terrain for wet slabs is on slopes where persistent slabs have been active in recent weeks and are now producing meltwater: east, west, and higher southeast aspects, especially in steeper, rockier terrain. You’ll find safer travel conditions while the upper snowpack is mostly frozen and supports your weight.  Move to colder aspects or lower slope angles to avoid the problem during the hotter parts of the day.  

     

    An example of a wet slab from last spring.  

Avalanche Discussion

Persistent slabs remain the most difficult problem to manage and can cause a dangerously large surprise.  On one hand, we saw unusually poor snowpack structures develop from prolonged drought and the big storm in February.  On the other hand, loading since February 20th has been relatively minor, allowing the layers to very slowly adjust and gain some strength underneath thick, hard slabs that are difficult to collapse.  Recent observations from Upper Cement and Brush Creek highlight poor structure and a higher likelihood of triggering an avalanche in parts of the Southeast Mountains. Further evidence comes from this destructive natural avalanche near Conundrum Creek during last Friday's storm, an area that often mirrors the shallower portions of our forecast zone. Recent observations from the Slate and this video from Gothic highlight improvements in deeper parts of the forecast area. Although you are more likely to find trouble near and east of town, land mines exist in both zones, and careful terrain choices are still essential.

Although there is some uncertainty among our forecast team, we listed wet slabs as a low-probability concern today, which may be more of an issue in the shallower parts of our forecast areas where freewater is more often closer to reaching weak layers.  It's a difficult problem to forecast, and one that forecasters are often behind the curve on.  Yesterday, we observed meltwater pooling near buried weak layers on a shoulder aspect, and last night's freeze will break down sooner due to some overnight cloud cover and warmer temperatures.  Although we expect more dramatic wet avalanches with the upcoming warmups (see Weather Tab), it's not a bad idea to start adjusting your travel habits now that meltwater is on the move.  On slopes that are getting wet today, the safest strategy is to start and finish early while the upper snowpack is locked up, especially on the most concerning aspects highlighted above. Be cautious around steep terrain below rock bands that heat quickly and can funnel meltwater into weak layers well before the snowpack feels saturated or unsupportive.

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