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

Expect a transitional day back to winter with increasingly strong winds at ridgeline and snowfall accumulating quickly later in the day. You may find touchy wind slabs at higher elevations. Chances are still low for triggering a hard persistent slab, but continue to be careful of treading into complex, or unsupported and shallow terrain on north to east facing slopes. 

Problemi valanghivi

  • Wind Slabs

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

    Winds are expected to be very strong and increase during the day. This, combined with snowfall that may start to accumulate by afternoon may create touchy windslab danger in alpine terrain. This is most likely to occur at higher elevations near the crest. Very strong winds will blast the high country, creating very stormy conditions. Watch out for blowing snow and accumulating snow. Exit steep, upper elevation slopes by the time these stormy conditions materialize in your chosen venue for the day.

    Example of small wind slab avalanche in wind affected, alpine terrain.

  • Persistent Slabs

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

    Snowpack tests have indicated that large persistent slab avalanches are still possible on shaded slopes above 5,000ft. Consider avoiding shallow, rocky, or very steep unsupported slopes. North and east aspects without supportable crusts near the surface may be the most likely areas to trigger a slab. Look for safe locations to stop and regroup, creating a buffer of distance between you, and larger start zones.  Keep in mind potential for cornices to fail, these could trigger larger slab avalanches on unsuspecting travelers below. Larger triggers such as snowmobiles or a group of people may trigger one of these slabs of older, stiffened snow.

    Indicators of persistent slabs are whumphing collapses and snowpack tests that pop or drop suddenly. Avoidance of slopes where we know the recipe exists for these avalanches is really the only way to be sure to stay safe, even though chances of triggering one of these may be low. You can dig down and find the late-January weak layers 1-2 feet below the surface.  In many areas, this layer is a combination of weak sugar-like facets sandwiched between two crusts. Sometimes you'll find weaker snow or old surface hoar above the upper crust. The weak layers are deepest near and west of the Cascade crest and in wind deposited zones. In the eastern part of the zone and in wind scoured areas, the crusts may be found near the surface.

    (2/5/2022)

    A skier triggered avalanche near Maple Pass. Three people were caught, one was carried over 400ft with no injuries. E, 6,600ft

    Photo: NWAC public obs

Avalanche Discussion

On Friday, observers came across a small (D1.5) recent natural windslab avalanche on a north-facing moraine above Wing Lake. An approaching winter storm will begin to affect the area by Saturday afternoon. Strong winds and lightly accumulating snowfall should buffet high elevations near Washington Pass as the day progresses. Needless to say, it won't be the most pleasant afternoon for a summit. Avalanche danger is expected to increase overnight into Sunday as new snow stacks up and winds continue. The Valentines Day crust is now buried by a few inches of newer snow in some areas, and may still be on the surface further east. Observers found weaker snow beneath and sometimes above this thin crust in high, shaded locations during the week. New snow may not bond very well with these weak, old snow surfaces. 

During the week observers have targeted the late January weak layer. The one thing in common is that most tests produced sudden collapse results. In general, shaded, northerly aspects are still showing the most potential for human triggered avalanches where the crust-facet sandwich is most defined and weakest. The most recent natural avalanche on this layer was a D1.5 on a rocky, unsupported east aspect, near treeline on Porcupine Peak (see photo). On Thursday and Friday, observers got propagating test results with extended columns and moderate force on N and E aspects between 5,700ft and 6,500ft. Last week, observers noted a cornice fall that triggered a large wind slab avalanche in rocky north-facing terrain. On  February 5th, a notable avalanche was triggered near Maple Pass on an east aspect, near treeline. The slide likely occurred on the late January PWL and involved 3 people, carrying one over 400ft. Widespread whumpfing, rolling collapses, and remote triggering of avalanches were all common last week, though these direct signs of instability have become less frequent in recent days. The recent warm temperatures have helped the snowpack and late January weak layer gain strength, but the instability continues to linger.

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