Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 7 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

New snow and strong winds have formed fresh, sensitive slabs up to several feet thick (ex. Irwin, Emmons), most commonly at higher elevations and in wind-loaded terrain. Beneath the recent snow, a lower-probability but higher-consequence old slab problem has been reawakened on some slopes by the recent load. Conservative terrain choices are essential to manage both the obvious and the hidden avalanche threats.  Both problems are smaller and less common at lower elevations.  

Problemi valanghivi

  • Wind Slabs

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

    Strong winds yesterday drifted the recent low-density snow into thicker and more cohesive slabs on leeward and cross-loaded terrain features.  These newly drifted slabs will be most sensitive where they formed over faceted weak layers, and thickest in terrain favored by northwest to north winds.  At higher elevations, choose wind-eroded or lower-angle slopes to avoid the problem.  Below treeline, watch for cross-drifted slabs from down-valley winds in open areas.  Wind-sheltered terrain often lacks instabilities in the new snow, though some smaller storm slabs still exist on colder aspects.  

    A large slab that likely ran on 1/25 in cross-loaded terrain of Mt. Baldy. (1/25/2026) Photo: Ben Pritchett/CAIC

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    New snow and windloading over the weekend added stress to weak layers buried several feet deep.  The pattern of old slabs is highly variable from previous wind events and avalanche activity, and can be difficult to assess.  Poor structures are most common on the north half of the compass, especially previously drifted terrain near and above treeline.  A triggered avalanche in the new snow can step down and cause a larger, harder-to-escape avalanche.  The most reliable way to manage this problem is by choosing slope angles less than 30 degrees.  Southerly aspects, low elevations, and heavily wind-eroded terrain typically offer fewer concerns, where old slabs are less common. 

    This pit was dug before the most recent storm on an east-facing aspect near treeline.  Propagating failures highlight the potential for avalanches to break in old, weak snow near the ground.  

Avalanche Discussion

The weekend storm introduced the newest slab-forming layer to our below-average snowpack. Today, I’ll simplify snowpack assessment and management into two distinct flavors of slab avalanches:

New, softer slabs that formed this weekend: Storm totals range from about 5" near town to as much as 25" in the Ruby Range. Following yesterday's strong wind event, slabs will be thicker, more cohesive, and often more sensitive in wind-loaded terrain, making wind slabs the primary concern today.  They'll be most common near and above treeline, but also formed at lower elevations subjected to downvalley winds. Lingering storm slabs in protected terrain remain possible where new snow overlies weak facets on colder aspects, particularly in snow-favored parts of the forecast zone. Bottom line: Manage for slabs in new and drifted snow. Expect them to become more dangerous and more widespread as you gain elevation into wind-loaded terrain and travel deeper into the Northwest Mountains snowbelt.

Old, harder slabs that formed earlier this year: This is a trickier and more stubborn step-down problem. Now well disguised beneath the new snow, it complicates snowpack assessments. The recent load has the potential to reactivate deeper weak layers, including Christmas facets and November depth hoar. Some strategies for managing the problem include avoidance (sticking to slopes less than 30 degrees), a clear understanding of where these old slabs are and aren't in the terrain, or choosing more forgiving terrain consequences in case of surprises. We have the highest confidence that these deeper slabs are absent on mid- to low-elevation southerly aspects, where stacked sun crusts limit slab formation, and at lower elevations in the shallower parts of the forecast area, where the snowpack fully faceted during the January drought.

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