Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Increasing winds are forming small, sensitive wind slabs at higher elevations.  Fresh drifts will be most dangerous above cliffs, trees, or in gullies. Watch for blowing snow and cracking underfoot or machine to warn you of unstable snow. In isolated cases, there's potential to trigger a much larger avalanche that breaks on deeper weak layers, most commonly on high elevation, wind-loaded slopes with variable snow depths.

Problemi valanghivi

  • Wind Slabs

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

    West to southwest winds increased overnight and began drifting snow into thin wind drifts that will be sensitive to human triggers today.  Any new snow today will add fuel for wind loading.  Watch for blowing snow and cracking underfoot to identify the problem. Wind slabs will be most common below high-elevation ridges or in cross-loaded gullies.  A small wind slab can get you in trouble if it drags you into rocks or trees, into a gulley, or other terrain traps.  You can avoid the problem by riding in wind-sheltered terrain.  

    Blowing snow on Whetstone yesterday afternoon (2/18).  This is an indication that fresh wind slabs are forming.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    Over the past 10 days, several large avalanches have failed on faceted weak layers in the lower snowpack.  These include a natural avalanche on Carbonate Hil on Thursday, and several human-triggered slides the previous week (Hunter Hill, Snowmass). Persistent slab activity has been rare this month and most problematic on wind-drifted slopes at higher elevations.  Be cautious of similar-looking terrain where wind drifting has stressed buried weak layers and formed hard slabs of varying thicknesses.  

    This large persistent slab failed up to 5 feet thick on weak snow deep in the snowpack.  The avalanche ran naturally on 2/16 on Carbonate Hill.

Avalanche Discussion

Although avalanche activity was quiet yesterday around Crested Butte, skiers triggered a few avalanches breaking on wind-drifted slopes yesterday on the Aspen side, D1 to D2 in size (Marble 1, Marble 2,  Maroon Bowl).   Instabilities involving last week's storm and wind drifting are expected to be unreactive or very isolated today.  A fresh round of wind slabs began forming last night and will continue to develop today under strong westerly winds.  Soft snow available for transport in the alpine is relatively minimal; thus wind slab formation is expected to be small and localized to leeward terrain with broad fetches on the upwind side. Wind drifting yesterday evening on Whetstone is a great example of terrain with a productive fetch. This is most common above treeline, and on a few near treeline slopes.  If we see more than a few inches of new snow today adding better fuel for winds to work with, wind slabs will become more widespread and the danger will also rise to Moderate near treeline.  All in all, it's a relatively small and easy problem to recognize, but something to manage in high-consequence terrain.    

On Thursday, wind loading triggered a destructive persistent slab on Carbonate Hill.  Our forecast team visited the site yesterday, and also found hard, propagating results on weak layers near the ground in a targeted stability test.   This month, the pattern of persistent slabs has been localized to higher-elevation wind-drifted slopes in the Southeast Mountains.  It's a low-likelihood issue that will not provide obvious feedback and is difficult to assess.  Slabs are thick and very hard, making it difficult for humans to trigger except from areas where slabs thin out at their margins or in rocky areas.  

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