Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Warm temperatures and some sun may increase the chances of triggering loose wet avalanches as the daytime progresses. Cornices may be touchy, and you could trigger large slab avalanches on steep slopes affected by the wind. Consider the consequences on steep or unsupported slopes where wind has stiffened the new snow into cohesive slabs. 

 

Problemi valanghivi

  • Loose Wet

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

    Warming temperatures and sun are expected to moisten snow surfaces on slopes just south of east through west. If you see rollerballs or moist snow surfaces, consider moving to lower-angled or more shaded terrain. Wet avalanches could come down from steep slopes, and you could trigger loose slides on them. Look for clues like rollerballs, and fresh fan shaped slides during the day. 

    Example loose wet avalanche activity on the south face in nearby West North zone. Photo: Lee Lazzara

  • Wind Slabs

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

    The new snow is bonding to old snow surfaces, but theres still a chance you could trigger a slab that's a couple feet deep. Slopes with large cornices above may be the more likely places to trigger a slab. If the snow appears textured or stiffened by the wind, use well supported terrain. Make sure to use safe travel techniques exposing only one person at a time to the hazard. 

    We're at the point when you may not get direct signs of instability before triggering a slide, but if you did it could be surprising. While you could probably travel on many slopes safely on Saturday, keep this in mind.

    (2/9/2023) Very large, recent avalanche in the neighboring East Central zone. Photo: Matt Primomo

Avalanche Discussion

Observers reported a fresh recent cornice fall that triggered an 18" deep, large avalanche on a northerly facing slope near Harts Pass on Friday. Others reported steep terrain was unreactive near Washington Pass. 

On Thursday, observers in the Silverstar and Varden creek drainages found test results indicating that the February 3rd interface is gaining strength and is becoming less of a problem for triggering avalanches. Earlier this week observers reported a number of large (up to size D3) avalanches throughout the Highway 20, Washington Pass area. Crowns were mostly in north to east facing terrain, below cliff bands or in other wind-loaded terrain. Many of these appear to have run on February 7th.

Almost 2 feet of snow accumulated from February 3-8th. Observers were able to trigger avalanches on the February 3rd interface just after the storm. On Wednesday, a triggered slide near the Lyal glacier stepped down to the new/old interface and broke into a large avalanche, 6,400ft, east aspect. On Sunday also near Rainy Lake, I found planar shear at the Feb 3rd interface at a profile site near treeline, though I couldn't produce similar results in a number of other quick tests near and below treeline.

There are a few layers that we've been tracking in the upper snowpack. Aside from the February 3rd interface, the Jan 5th surface hoar (about 2-3ft below the surface) had previously been widespread and problematic in snowpack tests. With time and rounding of the grains, this layer is likely gaining strength. At a profile on Sunday above Rainy Lake, test results indicated that the layer was not a problem for avalanches at that location. Elsewhere, especially in the eastern mountains, it could still be an issue if you cross a shallow part of a loaded slope.

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