Bollettino valanghe

West Slopes Central

Northwest 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

Strong winds and light snow on Monday could build fresh wind slabs on top of existing unstable slabs. Steer around steep, wind loaded slopes in favor of lower angle terrain to reduce the risk of triggering an avalanche. The threat of isolated - but large and surprising - avalanches could persist at upper elevations for the foreseeable future. 

Problemi valanghivi

  • Wind Slabs

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

    Strong winds plus light snowfall could build fresh wind slabs on Monday above the current crop of unstable slabs. Anticipate higher than forecast danger and deeper, more widespread wind slabs if there is more than 6” of new snow and/or you observe extensive wind transport. The highest snowfall totals could be in the southern portion of West Central related to a convergence zone.

    The existing surface of dense snow makes it a bit harder to distinguish areas of wind slab. You may see active wind loading as you travel. Also, reference cornices and wind affected snow surfaces to identify areas of potential loading. 

    Hand shears, test slopes, and track tests are probably the best way to evaluate wind slab reactivity as you travel. Approach wind loaded slopes with caution and use areas of lower angle, supported terrain to navigate around steeper areas where you are more likely to trigger an avalanche.  

     

    (2/6/2022)

    Snowmobile triggered wind slab avalanche at Schriebers/Mt. Baker. Southeast aspect at 6200'. Note cornices directly above crown indicating wind loading on the slope.

    Photo: Graham Clark

  • Persistent Slabs

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

    January's dry spell created weak layers of sugary facets and old crusts that are now buried 1-2’ feet deep. In neighboring zones a large snowmobile triggered avalanche on Saturday, a large natural on Mt. Baker, plus two remotely triggered avalanches in the last week have been linked back to these layers. Reports of extensive whumphing have been noted throughout both West North and Steven Pass zones. 

    Persistent avalanche problems are tricky - there is a low likelihood of triggering but if you do and get caught? The outcome will not be good.  So what to do about it? First don't ignore obvious signs of instability like whumphing, shooting cracks, or previous avalanche activity where you identify old crusts in the bed surface. Minimize travel on steep slopes at upper elevations and remember persistent slab avalanches can be triggered from low on the slope or remotely. When assessing terrain, factor in not only the possibility of triggering a large avalanche but also the consequences in the terrain below if you are caught. 

    (2/6/2022)

    Large natural avalanche (D2.5) that released in or above crust-facet layering buried in late-January. Old rain runnels/rills are visible in the crust bed surface. East aspect at 6400' on the south side of Mt. Baker

    Photo: Graham Clark

Avalanche Discussion

Light rain at lower elevations Monday could trigger another round of pinwheels, rollerballs, and small loose wet avalanches on all aspects. Remain aware of what is above you, especially if rainfall is stronger or lasts longer than expected.

Additional skier and snowmobile triggered wind slab avalanches were reported on Sunday in West North despite over 24 hours since the last wind loading. These were all reported releasing within layers of new snow and most were around 1’ deep. Though weather conditions are favorable for bonding, it may take longer than usual. This is due to pronounced strong over weak layering where the dense wind slabs (pencil hard snow) rest on much weaker snow (4 finger hard snow) that fell at colder temperatures in early February. This layering is also suspected to be behind the wide propagation of the many human triggered wind slabs.

Avalanches and other signs of instability related to deeper crust-facet layering also continue. On the other hand, snowpack test results vary widely and plenty of slopes where the problem exists have been skied and ridden. Despite the uneven distribution of this problem a bit of a pattern is emerging. All avalanches and most whumphs have been on more northerly terrain, likely because strong sun in late January melted the layers in question into a single stout crust. Also, the problem seems to be restricted to higher elevations. Crust-facet layers and other weak snow surfaces were found at all elevations during the January dry spell. Rain and very wet new snow that fell on January 30th may have wetted and ultimately strengthened these layers. Observations above 5000’ in neighboring zones have found faceted layers drier and weaker.

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