Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Last night's snow squall also rolled in with gale-force winds. SW to NW winds hit 90mph at 12,000 and 50mph at 11,000ft. The best guess on new snow accumulations at 5am is in the 2 to 6" range across the whole forecast area. The snowy landscape will have changed after this extreme wind event. More natural avalanches are expected to have released last night, while other slopes may just be hanging on the edge. Dangerous avalanche conditions prevail. Especially on recently wind-loaded slopes, and more generally on slopes greater than about 30 degrees facing west to north to east. With high temperatures in the single digits, don't let yourself rush the decision-making process. The travel advice remains to stay conservative and cautious with your terrain selection. 

Lawinenprobleme

  • Persistent Slabs

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

    To avoid getting caught in a dangerous persistent slab avalanche today, choose low slope angles or seek out sunnier aspects.   In the past week, there has been a constant stream of natural and human-triggered slab avalanches breaking on faceted weak layers near the ground.  The problem is serious: recent incidents include a helicopter evacuation and a fatality.   Be wary of traveling below steep, connected slopes because many of these avalanches have been triggered remotely from adjacent low angle terrain.  Persistent slabs have been most active on slopes steeper than 35 degrees that face west through north through east at all elevations, and in a few cases, high southeast aspects.  If you are traveling on a slope that fits that description, expect to trigger an avalanche easily if it hasn't already avalanched earlier this week.  Slabs are generally one foot thick below treeline and will be denser and thicker as you gain elevation towards wind loaded terrain features.  

    12/19: Persistent slab avalanches can be remotely triggered, meaning you don't need to be on the steep portion of the slope to trigger them. Here's an example from Coneys.

  • Wind Slabs

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

    Recent extreme winds blew from the southwest to the west and now remain strong from the north. These wind will have removed snow from windward terrain features, combined it with the recent new snow, and build wind slabs on the lees sides of terrain features. Below treeline elevations are even in the mix, with down-valley winds building fresh slabs on cross-loaded terrain. This avalanche problem may also exist in unusual locations given the character of this wind event. These slabs may release up to about 15" thick, or further step down into the Persistent Slab avalanche problem where the two problems overlap. 

Avalanche Discussion

Measuring the new snow accumulations after a wind event like this is really just best guessing. Those winds will have removed the new snow from some weather stations, and potentially deposited it at other weather stations. As of 5am Schofield Pass is showing a snow height increase of about 5 to 6", but no real gains in SWE. Irwin weather station showed a snow height increase around 4", CBMR pow cam had about 4", and Upper Taylor also increased by about 4". 

The peak winds came during the snowsquall yesterday evening. Those southwest to west winds, have now become north and will remain out of the north for the rest of the day. Those north winds are also expected to increase a bit this afternoon. We can definitely expect changes to the snowpack and snow coverage after such an event. For example, just how much snow is left on mid to upper elevation slopes facing west to north? We may have changes to the distribution of the Persistent Slab avalanche problem in the coming days due to some of these slopes having been destroyed by the winds, and others being further loaded. 

December has been characterized by dangerous avalanche conditions, hundreds of avalanches, avalanche accidents, and lost members of the community. The current snowpack was built on an exceptionally weak foundation in many areas. Last night's loading event will have again stressed these weak layers and we are still in a holding pattern with these conditions. 

Staying warm will be key, while riding protected slopes today. Signs of instability may not be as obvious as the past days, thanks to thick or dense slabs, even in sheltered terrain. Where the persistent slab avalanche problem exists, it's recommended to keep those slope angles to near or below 30 degrees, and avoiding high consequence terrain. There may still be some nice turns to be made on south-facing terrain, just keep an eye out for wind slabs in usual locations and for potential crusty conditions under the new snow after the last few days of warm temps. 

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