Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

Pay attention as you gain elevation and transition into wind-affected terrain where avalanches will be the largest and easiest to trigger. New and wind drifted snow may be poorly bonded to variable and firm old snow surfaces. Choose simple, supported terrain as the snowpack takes time to adjust.

Problemi valanghivi

  • Wind Slabs

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

    Backcountry travelers easily triggered avalanches in wind drifted snow in leeward terrain since the storm began on 1/30. These slides failed at the base of the new snow and slid on the firm icy crust below. Some even propagated the width of the features in small terrain. That signals that bigger slopes may be capable of producing much larger avalanches. Similar conditions are expected Wednesday as cool temperatures, light snowfall, and strong winds continue. It will take additional time for slabs of wind drifted snow to bond to the underlying hard snow. Be patient as the snowpack takes time to heal, and look for clues like fresh drifts, blowing snow, and wind textured surfaces to help anticipate which slopes are wind-loaded. Choose lower-angle terrain and slopes sheltered from the wind to reduce your risk.

    (1/31/2022)

    This small wind slab was intentionally triggered by a skier on a NE aspect around 6300'. The avalanche failed at the new-old snow interface. HS-ASc-R1-D1-I. 

    Photo: Shane Robinson

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    A variety of weak snow surfaces and icy crusts were reported prior to this storm and are now buried by 8-12in of new snow. You may see that avalanches fail at the base of the new snow or on layers created by the storm. While you can use small slopes and hand pits to investigate the recent snow, the complex variability will make it challenging to identify patterns and make accurate assessments. What you find on one slope may be different from the next, so build in a wide margin for error. Choose smaller lower consequence slopes until we know more about how these layers fared during the storm. Also keep in mind that in steep unsupported terrain, the cold dry snow may remain cohesionless and sluff off rocks and cliffs, and run far and fast downslope.

    (1/28/2022)

    Large surface hoard and small near surface facets were seen on a variety of slopes in the Crystal backcountry. These grains were typically seen on NW-NE aspect, but could be found in any shaded area.

    Photo: Dallas Glass

Avalanche Discussion

NWAC forecasters traveled in the Crystal backcountry Tuesday and reported variable conditions. Uncertainty regarding the 1/30 interface forced conservative terrain choices. Although no new avalanches were observed, weak snow was easy to find in the upper snowpack (video below). Blowing snow was widespread, and wind slabs were growing in size and distribution. Evidence of strong and erratic winds was widespread with wind slab development further down slopes than what is typically observed, and some windward areas scoured down to bare ground.

Prior to this storm, numerous observers reported near-surface facets, facet-crust sandwiches, icy crusts, and surface hoar across the zone. In general, firm crusts were found on more southerly aspects, while facets and facet-crust combos were seen on shadier slopes. Because these layers are relatively shallow, they should be easy to find with simple observations as you travel. However, the variability will make decision-making uncertain. Fortunately, below this most recent interface, the snowpack is very strong and well settled. Currently, we don’t have any significant layers of concern deeper in the snowpack. We expect any avalanches to occur near or above the 1/30 interface.

Regioni coperte