Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

An unusual wind loading pattern is adding additional load to the persistent slab avalanche problem on westerly and northerly facing slopes. The most likely areas to trigger this persistent slab avalanche problem are trigger points, and where the total snowpack depth is relatively shallow between about 80cm and 140cm deep. Small wind slabs are further possible to trigger on the lee sides of terrain features, and in wind-sheltered areas, you can encounter dry loose avalanches on steep northerly-facing slopes. Careful evaluation is required to identify the terrain that is a concern for these avalanche problems.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    In the Southeast Mountains, slabs breaking on older weak layers are becoming more difficult to trigger but remain a concern on many slopes.  The most prominent and active weak layers are surface hoar and facets buried a couple feet deep on the north half of the compass. There is also smaller potential for avalanches to break on faceted crust layers on some higher, southerly aspects or depth hoar layers near the ground.  Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.  Avalanches breaking into old weak layers are unlikely on mid to low elevation, southerly aspects where there are strong crusts in the upper snowpack.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem.

    This large avalanche was remotely triggered in West Brush Creek on March 8th. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Over the last 24 hours, the wind direction has been out of the east to southeast and those winds have formed small wind slabs on the lee sides of terrain features. Make a plan to manage this avalanche problem before committing to bigger avalanche terrain. Pillowy-looking snow deposits will help you clue into the local wind-loading patterns in your area and small test slopes can help refine the potential avalanche size. Earlier this week, we had wind loading occurring from westerly and northerly winds, so be prepared for more isolated wind slabs around the rest of the compass. 

    A small wind slab on the lee side of a cross-loaded terrain feater. Mt Axtell, 3/14.

Avalanche Discussion

Remote weather stations such as Scarps Ridge and Cinimmion Mountain are not capturing the recent winds very well. The weather station at 11,000ft on CBMR is highlighting the recent easterly winds the best, with average wind speeds in the teens to twenties and gusts in the twenties to thirties. Light snow accumulations through the week have kept small to moderate amounts of snow available for transport into our current wind slab avalanche problem. We rarely see easterly winds, so remember these wind-loading patterns are not what we typically encounter. Wind slabs are currently driving the avalanche danger rating in the NW Mountains while the persistent slab avalanche problem continues to drive the danger in the SE Mountains. 

The freezing level looks like it will climb to around 10,000ft today. If the cloud cover is thin enough, we may get some greenhouse weather and moist snow surfaces on southerly-facing slopes. 

The snowfall over the past few days is gradually adding small amounts of stress to our persistent slab problem. The pattern of triggered and natural persistent slab avalanches over the past 2 weeks clearly points to areas with shallower snowpacks being the most problematic. Most of the avalanche activity has been in the shallower part of our forecast area (the Southeast Mountains), and the few persistent slabs in the deeper zone occurred on windward slopes or on slopes that have repeatedly avalanche this season keeping the snow depth unusually shallow. This avalanche problem has the lowest likelihood of triggering in consistently deep snowpacks (>200cm). This video of a recent persistent slab on Gothic shows how shallow spots and variable snow depths are more common in wind-affected, alpine terrain.

CBAC Event:  Don't forget the 50th Al Johnson Race is this Sunday, March 17th.  Registration and information can be found at cbavalanchecenter.org.  All proceeds to benefit the CBAC.

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