Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The storm snow should start to heal on Thursday, but avalanches could involve all of the new powder. Some of these slides could trigger very easily and run quickly. Any steep open slope should be suspect regardless of its aspect or elevation.

Problemi valanghivi

  • Storm Slabs

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

    Natural and triggered avalanches occurred on Wednesday. Most (if not all) of these slides failed on the 1/16 interface. At least in some spots, weak near surface facets were the culprit. These storm slabs might not heal quite as quickly. You may still trigger avalanches where the snow overlays facets, on steep convex rollovers, in unsupported terrain, and where the wind creates deeper drifts. 

    Quick hand pits, small slopes, and uptrack tests can all demonstrate how these storm slabs will fail. However, snow surfaces were quite variable before this storm. Facets and surface hoar were not uniform across the landscape. This could make determining how any particular slope will reach quite challenging.

    (1/17/2024)

    This avalanche failed sympathetically to an adjacent slope during avalanche mitigation on I90. 

    Photo: Wash DOT SCR

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    It’s still there. The soft powder snow didn’t make it go away. The question isn’t the snowpack structure, we know it’s bad. The question is, "will it trigger?"

    Weak facets sit within a crust matrix about 3-4ft (1m) below the surface and still fail predictably in snowpack tests. A small storm slab, cornice fall, or finding the weak spot in the snowpack could be all that’s needed to make an entire large slope come unglued. 

    We don’t have a lot of confidence in this problem, but you should consider it and the potential consequences before spending time traveling through any part (start zone, track, and runout) of bigger avalanche paths.

    (1/10/2024)

    This very large avalanche released using explosives during avalanche control at Alpental. It is an indication that deeply buried weak layers could still be active. 

    Photo: Alpental Ski Patrol

Avalanche Discussion

After a wild stormy day on Wednesday, things should quiet down a bit. Another 4-8in of snow could bring storm totals to 12-18in in the zone. In a sense, we’re talking about the new snow healing (decrease in likelihood) but potential slabs getting bigger (increase in size and consequence).

NWAC forecasters, Alpental Patrol, and WA DOT all reported similar conditions on Wednesday in various parts of the Pass. Very shallow slabs grew in size and reactivity during the day. Numerous D1-1.5 natural, skier triggered, and explosive triggered slides were reported. One avalanche released sympathetically to a nearby slope. Signs of instability like that could suggest near surface facets. 

Deeper in the snowpack, we targeted the Solstice Facet/Crust complex. Very weak needly facets (see photo) failed suddenly in snowpack tests (4800ft, WNW). This persistent weak layer is not confidence-inspiring. 

In short, the avalanche concerns could be summarized into three layers: 1). Instabilities within the new snow, 2). The 1/16 interface, and 3). The Solstice Matrix.

Regioni coperte