Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Yesterday eeked out just 4-inch storm totals.  Strong northwesterly winds drifted that new snow and slightly increased the burden on weak layers lower in the snowpack.  Reports of cracking, collapsing, and a large, remotely-triggered avalanche came into the CBAC yesterday.  Signs of instability persist.  Slopes that show evidence of recent drifting are most concerning, but even more sheltered terrain that faces west through north through east continues to offer a likely chance for you to trigger an avalanche.  You can reduce your risk of triggering an avalanche by selecting lower-angled terrain that is not connected to or beneath steeper terrain, and thoughtfully selecting aspects where avalanches are less likely.  A conservative mindset and route plan will serve you well.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    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.  

    12/23 - A remotely-triggered avalanche below treeline at the head of the Slate River Valley.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1

    Recent extreme winds blew from the southwest to the west and now, Wednesday and Thursday, from the northwest. These wind will have removed snow from windward terrain features 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 12" thick, or further step down into the Persistent Slab avalanche problem where the two problems overlap. 

    Example of a small Wind Slab (not a recent photo)

Avalanche Discussion

The latest round of snowfall was meager with totals only reaching up to the 4-inch range.  Measuring snow totals during wind events is difficult, but just enough snow fell that strong winds were capable of keeping the pressure on weak layers on drifted features.  The most suspect terrain will be drifted slopes on the east half of the compass (NE-E-SE).  You can likely find fresh Wind Slabs here, but the more concerning problem is the underlying Persistent Slab avalanche problem.  Terrain that you know contains deeper weak layers should be managed for the Persistent Slab problem, not the surface Wind Slab.  Triggering a Wind Slab would likely result in a "step-down" avalanche to lower weak layers where it overlaps with Persistent Slab structure.  South and Southwest terrain where you are less likely to find a Persistent Slab problem are slopes where managing for a Wind Slab avalanche would be prudent.  You may be able to find fresh Wind Slabs behind ribs or pressed into gullies on south and southwest features at upper elevations.

The Persistent Slab problem continues to collapse, crack, and produce avalanches.  Yesterday, forecasters remotely-triggered a dangerous avalanche below treeline at the head of the Slate River Valley.  For areas in the Northwest Mountains and terrain along the border in the Southeast Mountains, these slabs are 1 to 2 feet thick in sheltered areas and much larger on drifted features.  Weak layers have been very slow to adjust to the slabs that have been forming over the past two weeks.  The simplest solution is to choose lower-angled slopes on terrain that faces west through north through east.  Slopes steeper than 35 degrees on these aspects without previous avalanche activity are the bullseye locations for you to trigger a dangerous avalanche.  Remember that under the current conditions there is the distinct potential for you to trigger an avalanche from immediately below steep slopes down on top of you.  Choose route plans with this possibility in mind.

Weather forecasts suggest that the snowpack will get a chance to catch its breath over the next few days.  As signs of instability diminish, and the snowpack slowly adjusts to the current slab burden, the avalanche danger rating may begin to drop for low elevation bands particularly for the Southeast Mountains where slabs are smaller.  For the time being, the evidence remains clear, you are likely to trigger a dangerous avalanche on steep slopes where the Persistent Slab problem is highlighted in the distribution rose. 

Regioni coperte