Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

New snow is slowly accumulating, and you could trigger freshly formed slabs at upper elevations. Check for instabilities at the new snow, old snow interface and in any area exposed to wind drifting. Increasing ridgetop winds may create dangerous conditions towards the end of the day.

Problemi valanghivi

  • Wind Slabs

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

    Observers noted shooting cracks and shallow slabs from a NE aspect above 5,000ft on Saturday. As new snow slowly adds up, winds are lightly drifting it into more cohesive slabs in higher, exposed locations. You could trigger slabs in areas with heavier drifting, and they could propagate a surprising distance on weak old interfaces. For the most part, these are likely to be fairly shallow. Increasing westerly winds the second half of the day should ratchet up the danger, and some alpine areas may become dangerous later in the day.  

    Look for clues to how wind-drifted snow may react before entering larger features. You can check to see what may happen with hand pits, skin track tests, and small test slopes. Look for shooting cracks and small slabs as indicators that you could trigger an avalanche.

    (2/4/2023)

    Shallow slab on a NE aspect at 5,300ft above Lake Valhalla on Saturday.

    Photo: Erin Reynolds

Avalanche Discussion

Aside from slab avalanches in wind exposed areas, warm daytime temperatures may turn snow surfaces moist at lower elevations. If the snow becomes sticky, or you see rollerballs occurring naturally from trees and on steep slopes, then expect you could trigger a small wet loose slide. 

The mountains are picking up some new snow again after a fairly lengthy mid winter dry spell. Observers reported 4-6" in the zone on Saturday. The longer the dry spell, often the less likely the new snow is to bond to old surfaces. This was about a week since the last snow, notable for early February on the crest of the Cascades. A blast of arctic air weakened many snow surfaces into near surface facets on shaded slopes (see photo below). The recently buried snow surfaces include a range of conditions including small near surface facets on sheltered northerly aspects, slick sun crusts on slopes that receive direct sun, and various degrees of stiff wind packed snow. Some areas held isolated patches of recently buried surface hoar on shaded slopes. Below 3,500ft you can expect old crust surfaces beneath any new snow. 

There are a couple crusts in the upper snowpack, one from January 27th (often thin and brittle) and a more stout, clear ice lens that formed around the MLK holiday weekend. This one is about 1 foot below the surface, and the cold and dry recent weather has contributed to weaker snow above and below it. As new snow begins to add up, this creates a weak structure that we'll have to watch closely. Check out my ob from Friday for a more in depth racap of what I foundout near Gemini Pass. 

Regioni coperte