Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Heavy snow and strong winds will increase avalanche danger. Reduce the risk of triggering an avalanche by sticking to lower angle, sheltered terrain and avoid travel under large, wind-loaded avalanche paths. Stormy weather could make for challenging conditions on Sunday morning.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–3

    A storm overnight into Sunday will drop 1-2’ - and maybe more - of new snow across the forecast zone. In addition to fresh storm slab layers, expect strong winds to transport snow and build thicker slabs on leeward slopes. Last week a layer of facets and surface hoar developed at the snow surface around West North. Strong winds on Saturday disturbed or destroyed these weak grains in most wind exposed terrain, but they could still exist in sheltered areas and produce avalanches when loaded with new snow. Natural and human triggered storm slabs are more likely during periods of intense snowfall and rising snow levels.

    In general, Sunday will be a day to avoid most avalanche terrain, especially as you climb out of treeline. Don’t ignore obvious signs of instability like shooting cracks, whumphs, or recent avalanche activity. Approach any steep slope with caution and remain aware of terrain above you. If snow levels creep up during the day expect to see wet avalanche activity at low elevations.

    Example of storm slab avalanche. Not the cracks above the crown where the slope was a little too low angle for the slab to slide.

Avalanche Discussion

A big change is underway in the North Cascades this weekend with a decent storm Sunday and then a warm, wet atmospheric river setting up early Monday. A glorious week of high pressure, cool temperatures, and good snow conditions is coming to a fitting end with a major reset in the next 24-48 hours.

Observation notes:

- Wind transport early Saturday was spotty with some terrain features seeing moderate transport while others saw little despite strong winds. This is likely due to sun crust on windward slopes locking in the snow and preventing transport. More transport was observed on the highest peaks where less crust formed in the last week.

- Strong winds stirred up the snow surface and dispersed faceted snow and surface hoar that formed during high pressure. That being said, wind affected surfaces still held the weak grains but the layer lacked continuity. In some protected start zones the surface layer was unaffected.

- The upper snowpack above the late-January crusts is not “weak” per se but is also not the bulletproof snowpack we often have prior to a storm. Suspect layering below breakable crust on south aspects, small facets around crusts buried February 14th and 19th and other layer interfaces are notable in snowpit observations. While testing shows these layers are not really interfaces we are worried about triggering, smaller storm and wind slab avalanches could step-down into these layers and produce very large avalanches.

- Dry snow above the late-January crusts could produce wet avalanches if snow levels end up being a bit higher with the atmospheric river event and rain falls near and above treeline.

 

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