Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Dangerous avalanche conditions Saturday will require a conservative mindset. Anticipate rising hazard throughout the day as additional loading from new snow and wind increase the size, depth, and likelihood of avalanches. Avoid wind loaded slopes 35 degrees and steeper, and use caution as the icy crust underlying recent snow remains a good sliding surface for avalanches. 

Problemi valanghivi

  • Wind Slabs

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

    Expect another 6-12in of new snow to accumulate by Saturday afternoon bringing snow totals over the past week to 2ft+. Human triggered avalanches in wind drifted snow were reported each day since Tuesday. Triggering an avalanche large enough to bury, injure, or kill a person will be likely on upper elevation, wind-loaded slopes 35 degrees and steeper. Previously formed wind slabs still need time to stabilize, and fresh slabs will grow in size and distribution with new snow and wind.  

    Pay attention as you transition into wind affected terrain and look and feel for sudden changes in snow surface texture and hardness. Fresh slabs rest atop slick and variable surfaces, and even weak, sugary snow in isolated areas. Look for obvious signs of instability like recent avalanches, shooting cracks, and collapses, and dial back your terrain choices if any of these red flags are present. Carefully assess how new snow has bonded to old snow surfaces as you travel using hand pits and small test slopes. Seek out lower angled and wind-sheltered terrain to reduce your risk.

    (1/28/2021) A skier triggered avalanche in new/wind drifted snow that broke about 1ft deep and ran on a crust layer. The avalanche occurred on a NW aspect at 4300ft in the Twin Sisters range. Photo: Matt Lubar

  • Loose Dry

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

    In areas sheltered from the wind, the incoming low-density snow will likely remain cohesionless. Loose snow avalanches or sluffs may run downhill on their own or easily be triggered by riders in steep terrain. These avalanches could run far and fast, and entrain enough snow to knock you off your feet, carry you into rocks or trees, or bury you in confined terrain. They may even trigger slab avalanches. Avoid exposure to steep slopes above and terrain features where avalanche debris can concentrate like gullies, benches, and depressions. 

    (1/29/2021) Small dry point releases in steep terrain on Mt. Herman. Photo: Simon Trautman

Avalanche Discussion

Since Sunday (1/24), 12-18in of new snow gradually accumulated throughout the West North Zone. Strong and shifting winds accompanied this incremental load of cold, low-density snow creating variable loading patterns. Natural and triggered avalanches (mostly D1, a few D2) were reported recently in many areas. Avalanches primarily occurred on upper elevation, wind-loaded slopes breaking 6-24in deep on slick underlying crusts and within new and wind drifted snow.

Carefully assess the snowpack as you travel, especially on the northern half of the compass where you might find layers of weak faceted snow associated with crusts buried 1-2ft by recent and windblown snow. These layers were the culprit in recent avalanches, including one remotely triggered by a skier (observation). Shooting cracks and collapses were also observed, along with sudden and propagating fractures in snowpack tests. There is uncertainty regarding the distribution and sensitivity of these buried weak layers. Evidence exists but is not always easy to find. Weak snow could be above and below the crusts, or not present at all. The variability may be the biggest challenge, so investigate each slope you plan to ride individually, as what you find in one area may be different from the next.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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