Bollettino valanghe

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

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

Elevated winds during and immediately after recent snowfall have formed problematic drifted slabs on leeward-facing terrain that warrant diligent evaluation versus blindly committing. Traveling on or directly below steep northerly and easterly-facing slopes at upper elevations increases your chance to find trouble. Steer clear of areas with a smooth, rounded appearance or where you see cracking in the snow to avoid a cascading scenario where a drifted slab provokes a larger, wider breaking avalanche that fails in deeper weak snow layers. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Steady winds and abundant low-density snow on the surface in windward-facing fetches creates prime conditions for the formation of wind-drifted slabs. Wind speeds in the last 24 hours have gradually diminished in the Southern Mountains, but unfortunately the damage has already been done. Fresh slabs that formed during Saturday’s storm and on Sunday before winds decreased need a little more time to find equilibrium before they are no longer sensitive to the weight of a rider or machine.

    Freshly drifted slabs have formed immediately downwind of ridgelines and around steep mid-slope terrain features like gully walls or cliff bands. Slab depths could vary across the same slope, but expect increasing slab depths as you move higher in elevation. Recent avalanche activity and poor stability test results continue to alert us to the threat of this problem at upper elevations.

    You know you’ve migrated on top of a drifted slab if you feel a density change underfoot, where the snow surface transitions from soft to firm. Other characteristics include a rippled or textured surface, or identified by a pillowy-shaped snow surface. If you encounter any one of these surface clues, simply steer yourself around those areas. Sticking to lower-angled or more sheltered slopes will help reduce your avalanche risk.

    An avalanche that failed in the new storm snow on December 26, 2025.

    Several natural and skier-triggered avalanches were reported across the Silver Valley-Bitterroots during the peak of snowfall. Similar conditions exist across all forecast zones.

    Photo: Idaho Panhandle Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–2.5

    Persistent weak layers responsible for lingering snowpack instabilities are slowly getting buried deeper in the snowpack. Even though these interfaces are showing initial signs of becoming less reactive, there is still a worrisome array of weak faceted grains surrounding multiple rain crusts. In recent days, these weak interfaces have been providing us with less and less feedback, meaning there will likely be no warning signs until a large, potentially deadly avalanche is triggered. The only way to know for sure what the structure looks like below you or how reactive it may be is to dig down and investigate. 

    Larger triggers like a machine trenching through the upper slab have a slightly higher potential to influence these weak layers than a human. Another scenario is a skier or rider finding a shallow, not-so-sweet spot on the slope like near rocky outcrops or in wind-scoured areas. Being exposed to a prolonged period of clear, cold weather conditions will allow these layers to continue to weaken. This creates a lower likelihood, higher consequence regime. Continue to make conservative terrain choices and avoid traveling in steeper, more challenging terrain to avoid an unexpected avalanche encounter.

    Recent stability tests revealed that facets surrounding different rain crusts are continuing to weaken and producing propagating failures.

    December 24, 2025.

    Photo: George LaGesse

Avalanche Discussion

After nearly two-months of steady rollercoaster-like weather, the Inland Northwest gets a chance to soak in some much-needed Vitamin D. The prior extended period wasn’t always cake and flowers, and delivered quite the array of excitement. A snowy October transitioned to a rainy November, then back to snow to start December. Then back-to-back historic Atmospheric River events reshaped the landscape and pinched our access into the mountains. Over the last couple of weeks, we’ve had to cut through a plethora of downed trees to assess the damage and learned the reality of how much snowpack we lost in the tussle of it all. Then around the holiday, and just in time for the bustling ski area crowds, Old Man Winter returned and gifted the mountains with some healthy snow.

Storm totals since December 26 range one to two feet across all forecast zones, and some higher elevation areas likely received closer to three feet of snow. Temperatures finally behaved for once and progressively lowered during the storm as precipitation engulfed the region. While this has made for improved surface conditions, it delivered a new flavor of avalanche hazard onto a snowpack with multiple interfaces of looming concern below. Concerns in the form of both thin and stout faceted rain crust where faceting around them has impressed our entire staff at how quickly they developed once buried. How reactive each one has been has varied greatly between our forecast zones and even within the same areas.

Several natural and skier-triggered avalanches have been reported recently in the Silver Valley-Bitterroots and snow safety teams in multiple areas have been able to provoke some large slides with explosives. These artificial triggers are important at this point since those operational snowpacks are very similar to the backcountry and have had hardly any snowpack disturbance or rider compaction prior. The majority of reported avalanches occurred in typical start zone areas - underneath ridgelines and where strong winds built stiffer slabs over softer snow layers, but confined to snow sitting on the Grinch crust buried on Christmas Eve. Despite the stormy period coming to an end, we expect lingering sensitivity for a bit longer in freshly drifted slabs - especially in places with new snow depths north of a foot deep.

Based on our limited field observations since the latest storm ended, it doesn’t appear that deeper persistent weak layers succumbed to the recent snow load. However, these weak interfaces remain and are  shallow enough that the upcoming period of clear, cold weather will likely help the slab above either gain strength or become more unconsolidated faster than these weak grains gain strength. This moves us into a period where signs of unstable snow will continue to diminish and wakening the monsters in the basement will become less likely, but not fully eliminated. If you are able to trigger a deeper failure, those slides will be much larger, more difficult to escape, and potentially deadly.

As the sun makes a return today and beyond, don’t let a bluebird powder day lure you into a potentially dangerous situation. Approach the mountains with a conservative mindset and stick to it. Low angle slopes that are sheltered from the wind offer excellent riding conditions - as long as they don’t reside directly below steep overhead hazards. Give the snowpack time to settle before stepping out onto or below slopes that are over 30 degrees, and curb the scarcity trap of fewer soft riding conditions days so far this season. The winter season is still young and plenty of days are ahead for fun backcountry recreation.

Regioni coperte